Showing papers in "Nature Energy in 2020"

Managing grains and interfaces via ligand anchoring enables 22.3%-efficiency inverted perovskite solar cells

Abstract: We acknowledge the use of KAUST Core Lab and KAUST Solar Center facilities. This work was supported by KAUST and the Office of Sponsored Research (OSR) under award no. OSR-2017-CRG-3380. F.G. is a Wallenberg Academy Fellow.

High-nickel layered oxide cathodes for lithium-based automotive batteries

Abstract: High-nickel layered oxide cathode materials will be at the forefront to enable longer driving-range electric vehicles at more affordable costs with lithium-based batteries. A continued push to higher energy content and less usage of costly raw materials, such as cobalt, while preserving acceptable power, lifetime and safety metrics, calls for a suite of strategic compositional, morphological and microstructural designs and efficient material production processes. In this Perspective, we discuss several important design considerations for high-nickel layered oxide cathodes that will be implemented in the automotive market for the coming decade. We outline various intrinsic restraints of maximizing their energy output and compare current/emerging development roadmaps approaching low-/zero-cobalt chemistry. Materials production is another focus, relevant to driving down costs and addressing the practical challenges of high-nickel layered oxides for demanding vehicle applications. We further assess a series of stabilization techniques on their prospects to fulfill the aggressive targets of vehicle electrification. The development of high-nickel layered oxide cathodes represents an opportunity to realize the full potential of lithium-ion batteries for electric vehicles. Manthiram and colleagues review the materials design strategies and discuss the challenges and solutions for low-cobalt, high-energy-density cathodes.

High-energy long-cycling all-solid-state lithium metal batteries enabled by silver–carbon composite anodes

Abstract: An all-solid-state battery with a lithium metal anode is a strong candidate for surpassing conventional lithium-ion battery capabilities. However, undesirable Li dendrite growth and low Coulombic efficiency impede their practical application. Here we report that a high-performance all-solid-state lithium metal battery with a sulfide electrolyte is enabled by a Ag–C composite anode with no excess Li. We show that the thin Ag–C layer can effectively regulate Li deposition, which leads to a genuinely long electrochemical cyclability. In our full-cell demonstrations, we employed a high-Ni layered oxide cathode with a high specific capacity (>210 mAh g−1) and high areal capacity (>6.8 mAh cm−2) and an argyrodite-type sulfide electrolyte. A warm isostatic pressing technique was also introduced to improve the contact between the electrode and the electrolyte. A prototype pouch cell (0.6 Ah) thus prepared exhibited a high energy density (>900 Wh l−1), stable Coulombic efficiency over 99.8% and long cycle life (1,000 times). Solid-state Li metal batteries represent one of the most promising rechargeable battery technologies. Here the authors report an exceptional high-performance prototype solid-state pouch cell made of a sulfide electrolyte, a high-Ni layered oxide cathode and, in particular, a silver–carbon composite anode with no excess Li.

Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures

Abstract: Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. Reliability of stability data for perovskite solar cells is undermined by a lack of consistency in the test conditions and reporting. This Consensus Statement outlines practices for testing and reporting stability tailoring ISOS protocols for perovskite devices.

Current status and future directions of multivalent metal-ion batteries

Abstract: Batteries based on multivalent metals have the potential to meet the future needs of large-scale energy storage, due to the relatively high abundance of elements such as magnesium, calcium, aluminium and zinc in the Earth’s crust. However, the complexity of multivalent metal-ion chemistries has led to rampant confusions, technical challenges, and eventually doubts and uncertainties about the future of these technologies. In this Review, we clarify the key strengths as well as common misconceptions of multivalent metal-based batteries. We then examine the growth behaviour of metal anodes, which is crucial for their safety promises but hitherto unestablished. We further discuss scrutiny of anode efficiency and cathode storage mechanism pertaining to complications arising from electrolyte solutions. Finally, we critically review existing cathode materials and discuss design strategies to enable genuine multivalent metal-ion-based energy storage materials with competitive performance. Batteries based on multivalent metal anodes hold great promise for large-scale energy storage but their development is still at an early stage. This Review surveys the main complexity arising from anodes, electrolytes and cathodes, and offers views on the progression path of these technologies.

Benchmarking the performance of all-solid-state lithium batteries

Abstract: Increasing the specific energy, energy density, specific power, energy efficiency and energy retention of electrochemical storage devices are major incentives for the development of all-solid-state batteries. However, a general evaluation of all-solid-state battery performance is often difficult to derive from published reports, mostly due to the interdependence of performance measures, but also due to the lack of a basic reference system. Here, we present all-solid-state batteries reduced to the bare minimum of compounds, containing only a lithium metal anode, β-Li3PS4 solid electrolyte and Li(Ni0.6Co0.2Mn0.2)O2 cathode active material. We use this minimalistic system to benchmark the performance of all-solid-state batteries. In a Ragone-type graph, we compare literature data for thiophosphate-, oxide-, phosphate- and polymer-based all-solid-state batteries with our minimalistic cell. Using fundamental equations for key performance parameters, we identify research targets towards high energy, high power and practical all-solid-state batteries. Considering the interdependence of performance measures and the lack of a basic reference system for all-solid-state batteries, Jurgen Janek and co-workers analyse literature performance data for major types of all-solid-state batteries and benchmark them against minimalistic reference cells.

Structural transformation of highly active metal–organic framework electrocatalysts during the oxygen evolution reaction

Abstract: Metal–organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER). Despite their promising catalytic activity, many fundamental questions concerning their structure−performance relationships—especially those regarding the roles of active species—remain to be answered. Here we show the structural transformation of a Ni0.5Co0.5-MOF-74 during the OER by operando X-ray absorption spectroscopy analysis and high-resolution transmission electron microscopy imaging. We suggest that Ni0.5Co0.5OOH0.75, with abundant oxygen vacancies and high oxidation states, forms in situ and is responsible for the high OER activity observed. The ratio of Ni to Co in the bimetallic centres alters the geometric and electronic structure of as-formed active species and in turn the catalytic activity. Based on our understanding of this system, we fabricate a Ni0.9Fe0.1-MOF that delivers low overpotentials of 198 mV and 231 mV at 10 mA cm−2 and 20 mA cm−2, respectively. Metal–organic frameworks (MOFs) are increasingly being explored for electrocatalytic oxygen evolution, which is half of the water splitting reaction. Here the authors show that, under reaction conditions, mixed metal oxyhydroxides form at the nodes of bimetallic MOFs, which are highly catalytically active.

Electrochemical reduction of nitrate to ammonia via direct eight-electron transfer using a copper–molecular solid catalyst

Abstract: Ammonia (NH3) is essential for modern agriculture and industry and is a potential energy carrier. NH3 is traditionally synthesized by the Haber–Bosch process at high temperature and pressure. The high-energy input of this process has motivated research into electrochemical NH3 synthesis via nitrogen (N2)–water reactions under ambient conditions. However, the future of this low-cost process is compromised by the low yield rate and poor selectivity, ascribed to the inert N≡N bond and ultralow solubility of N2. Obtaining NH3 directly from non-N2 sources could circumvent these challenges. Here we report the eight-electron direct electroreduction of nitrate to NH3 catalysed by copper-incorporated crystalline 3,4,9,10-perylenetetracarboxylic dianhydride. The catalyst exhibits an NH3 production rate of 436 ± 85 μg h−1 cm−2 and a maximum Faradaic efficiency of 85.9% at −0.4 V versus a reversible hydrogen electrode. This notable performance is achieved by the catalyst regulating the transfer of protons and/or electrons to the copper centres and suppressing hydrogen production. Electrochemically reducing nitrogen-containing molecules could provide less energy-intense routes to produce ammonia than the traditional Haber–Bosh process. Here the authors use a catalyst comprising Cu embedded in an organic molecular solid to synthesize ammonia from nitrate ions.

Molecular design for electrolyte solvents enabling energy-dense and long-cycling lithium metal batteries

Abstract: Electrolyte engineering is critical for developing Li metal batteries. While recent works improved Li metal cyclability, a methodology for rational electrolyte design remains lacking. Herein, we propose a design strategy for electrolytes that enable anode-free Li metal batteries with single-solvent single-salt formations at standard concentrations. Rational incorporation of –CF2– units yields fluorinated 1,4-dimethoxylbutane as the electrolyte solvent. Paired with 1 M lithium bis(fluorosulfonyl)imide, this electrolyte possesses unique Li–F binding and high anion/solvent ratio in the solvation sheath, leading to excellent compatibility with both Li metal anodes (Coulombic efficiency ~ 99.52% and fast activation within five cycles) and high-voltage cathodes (~6 V stability). Fifty-μm-thick Li|NMC batteries retain 90% capacity after 420 cycles with an average Coulombic efficiency of 99.98%. Industrial anode-free pouch cells achieve ~325 Wh kg−1 single-cell energy density and 80% capacity retention after 100 cycles. Our design concept for electrolytes provides a promising path to high-energy, long-cycling Li metal batteries. The realization of the full potential of Li metal batteries requires high-performance electrolytes. Here Z. Bao and colleagues develop low-concentration electrolytes with a single-solvent and single-salt formulation, offering promise for high-energy and long-cycling batteries.

Realizing high zinc reversibility in rechargeable batteries

Abstract: Rechargeable zinc metal batteries (RZMBs) offer a compelling complement to existing lithium ion and emerging lithium metal batteries for meeting the increasing energy storage demands of the future. Multiple recent reports have suggested that optimized electrolytes resolve a century-old challenge for RZMBs by achieving extremely reversible zinc plating/stripping with Coulombic efficiencies (CEs) approaching 100%. However, the disparity among published testing methods and conditions severely convolutes electrolyte performance comparisons. The lack of rigorous and standardized protocols is rapidly becoming an impediment to ongoing research and commercialization thrusts. This Perspective examines recent efforts to improve the reversibility of the zinc metal anode in terms of key parameters, including CE protocols, plating morphology, dendrite formation and long-term stability. Then we suggest the most appropriate standard protocols for future CE determination. Finally, we envision future strategies to improve zinc/electrolyte stability so that research efforts can be better aligned towards realistic performance targets for RZMB commercialization. Zinc metal batteries (ZMBs) provide a promising alternative to lithium metal batteries but share the formidable challenges in reversibility. The authors discuss the key performance metrics of ZMBs and propose a protocol to assess the true reversibility of zinc metal anodes.

Electrolyte design for LiF-rich solid–electrolyte interfaces to enable high-performance microsized alloy anodes for batteries

Abstract: Lithium batteries with Si, Al or Bi microsized (>10 µm) particle anodes promise a high capacity, ease of production, low cost and low environmental impact, yet they suffer from fast degradation and a low Coulombic efficiency. Here we demonstrate that a rationally designed electrolyte (2.0 M LiPF6 in 1:1 v/v mixture of tetrahydrofuran and 2-methyltetrahydrofuran) enables 100 cycles of full cells that contain microsized Si, Al and Bi anodes with commercial LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathodes. Alloy anodes with areal capacities of more than 2.5 mAh cm−2 achieved >300 cycles with a high initial Coulombic efficiency of >90% and average Coulombic efficiency of >99.9%. These improvements are facilitated by the formation of a high-modulus LiF–organic bilayer interphase, in which LiF possesses a high interfacial energy with the alloy anode to accommodate plastic deformation of the lithiated alloy during cycling. This work provides a simple yet practical solution to current battery technology without any binder modification or special fabrication methods. Chunsheng Wang and colleagues develop an electrolyte strategy to enable the use of commercially available microsized alloys, such as Si–Li, as high-performance battery anodes. They ascribe its success to the formation of robust LiF-rich layers as the solid–electrolyte interface.

Dynamic stability of active sites in hydr(oxy)oxides for the oxygen evolution reaction

Abstract: The poor activity and stability of electrode materials for the oxygen evolution reaction are the main bottlenecks in the water-splitting reaction for H2 production. Here, by studying the activity–stability trends for the oxygen evolution reaction on conductive M1OxHy, Fe–M1OxHy and Fe–M1M2OxHy hydr(oxy)oxide clusters (M1 = Ni, Co, Fe; M2 = Mn, Co, Cu), we show that balancing the rates of Fe dissolution and redeposition over a MOxHy host establishes dynamically stable Fe active sites. Together with tuning the Fe content of the electrolyte, the strong interaction of Fe with the MOxHy host is the key to controlling the average number of Fe active sites present at the solid/liquid interface. We suggest that the Fe–M adsorption energy can therefore serve as a reaction descriptor that unifies oxygen evolution reaction catalysis on 3d transition-metal hydr(oxy)oxides in alkaline media. Thus, the introduction of dynamically stable active sites extends the design rules for creating active and stable interfaces. Understanding what underpins the activity and stability of oxygen evolution catalysts is an ongoing issue in the field of water splitting. Now, researchers show that balancing the rate of Fe dissolution and deposition over a metal hydr(oxy)oxide host yields dynamically stable Fe active sites, with the Fe–host interaction key to the performance.

Electrolysis of low-grade and saline surface water

Abstract: Powered by renewable energy sources such as solar, marine, geothermal and wind, generation of storable hydrogen fuel through water electrolysis provides a promising path towards energy sustainability. However, state-of-the-art electrolysis requires support from associated processes such as desalination of water sources, further purification of desalinated water, and transportation of water, which often contribute financial and energy costs. One strategy to avoid these operations is to develop electrolysers that are capable of operating with impure water feeds directly. Here we review recent developments in electrode materials/catalysts for water electrolysis using low-grade and saline water, a significantly more abundant resource worldwide compared to potable water. We address the associated challenges in design of electrolysers, and discuss future potential approaches that may yield highly active and selective materials for water electrolysis in the presence of common impurities such as metal ions, chloride and bio-organisms. Production of hydrogen fuel by electrolysis of low-grade or saline water, as opposed to pure water, could have benefits in terms of resource availability and cost. This Review examines the challenges of this approach and how they can be addressed through catalyst and electrolyser design.

Understanding and applying coulombic efficiency in lithium metal batteries

Abstract: Coulombic efficiency (CE) has been widely used in battery research as a quantifiable indicator for the reversibility of batteries While CE helps to predict the lifespan of a lithium-ion battery, the prediction is not necessarily accurate in a rechargeable lithium metal battery Here, we discuss the fundamental definition of CE and unravel its true meaning in lithium-ion batteries and a few representative configurations of lithium metal batteries Through examining the similarities and differences of CE in lithium-ion batteries and lithium metal batteries, we establish a CE measuring protocol with the aim of developing high-energy long-lasting practical lithium metal batteries The understanding of CE and the CE protocol are broadly applicable in other rechargeable metal batteries including Zn, Mg and Na batteries Coulombic efficiency (CE) has been frequently used to assess the cyclability of newly developed materials for lithium metal batteries The authors argue that caution must be exercised during the assessment of CE, and propose a CE testing protocol for the development of lithium metal batteries

All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant

Abstract: Monolithic all-perovskite tandem solar cells offer an avenue to increase power conversion efficiency beyond the limits of single-junction cells. It is an important priority to unite efficiency, uniformity and stability, yet this has proven challenging because of high trap density and ready oxidation in narrow-bandgap mixed lead–tin perovskite subcells. Here we report simultaneous enhancements in the efficiency, uniformity and stability of narrow-bandgap subcells using strongly reductive surface-anchoring zwitterionic molecules. The zwitterionic antioxidant inhibits Sn2+ oxidation and passivates defects at the grain surfaces in mixed lead–tin perovskite films, enabling an efficiency of 21.7% (certified 20.7%) for single-junction solar cells. We further obtain a certified efficiency of 24.2% in 1-cm2-area all-perovskite tandem cells and in-lab power conversion efficiencies of 25.6% and 21.4% for 0.049 cm2 and 12 cm2 devices, respectively. The encapsulated tandem devices retain 88% of their initial performance following 500 hours of operation at a device temperature of 54–60 °C under one-sun illumination in ambient conditions. Ensuring both stability and efficiency in mixed lead–tin perovskite solar cells is crucial to the development of all-perovskite tandems. Xiao et al. use an antioxidant zwitterionic molecule to suppress tin oxidation thus enabling large-area tandem cells with 24.2% efficiency and operational stability over 500 hours.

Light-driven methane dry reforming with single atomic site antenna-reactor plasmonic photocatalysts

Abstract: Syngas, an extremely important chemical feedstock composed of carbon monoxide and hydrogen, can be generated through methane (CH4) dry reforming with CO2. However, traditional thermocatalytic processes require high temperatures and suffer from coke-induced instability. Here, we report a plasmonic photocatalyst consisting of a Cu nanoparticle ‘antenna’ with single-Ru atomic ‘reactor’ sites on the nanoparticle surface, ideal for low-temperature, light-driven methane dry reforming. This catalyst provides high light energy efficiency when illuminated at room temperature. In contrast to thermocatalysis, long-term stability (50 h) and high selectivity (>99%) were achieved in photocatalysis. We propose that light-excited hot carriers, together with single-atom active sites, cause the observed performance. Quantum mechanical modelling suggests that single-atom doping of Ru on the Cu(111) surface, coupled with excited-state activation, results in a substantial reduction in the barrier for CH4 activation. This photocatalyst design could be relevant for future energy-efficient industrial processes. Syngas is a mixture of CO and H2 that can be converted into a variety of fuels. Syngas can be produced thermocatalytically from CH4 and CO2, but this requires high temperatures and coke formation can be a problem. Here the authors demonstrate lower temperature, light-driven production of syngas using a coke-resistant plasmonic photocatalyst.

Six-junction III–V solar cells with 47.1% conversion efficiency under 143 Suns concentration

Abstract: Single-junction flat-plate terrestrial solar cells are fundamentally limited to about 30% solar-to-electricity conversion efficiency, but multiple junctions and concentrated light make much higher efficiencies practically achievable. Until now, four-junction III–V concentrator solar cells have demonstrated the highest solar conversion efficiencies. Here, we demonstrate 47.1% solar conversion efficiency using a monolithic, series-connected, six-junction inverted metamorphic structure operated under the direct spectrum at 143 Suns concentration. When tuned to the global spectrum, a variation of this structure achieves a 1-Sun global efficiency of 39.2%. Nearly optimal bandgaps for six junctions were fabricated using alloys of III–V semiconductors. To develop these junctions, it was necessary to minimize threading dislocations in lattice-mismatched III–V alloys, prevent phase segregation in metastable quaternary III–V alloys and understand dopant diffusion in complex structures. Further reduction of the series resistance within this structure could realistically enable efficiencies over 50%. Stacking multiple junctions with different bandgaps and operating under concentrated light allows solar cells to reach efficiencies beyond the limits of standard devices. Geisz et al. present a six-junction solar cell based on III–V materials with a 47.1% efficiency—the highest reported to date.

Ligand-assisted cation-exchange engineering for high-efficiency colloidal Cs1−xFAxPbI3 quantum dot solar cells with reduced phase segregation

Abstract: The mixed caesium and formamidinium lead triiodide perovskite system (Cs1−xFAxPbI3) in the form of quantum dots (QDs) offers a pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective oleic acid (OA) ligand-assisted cation-exchange strategy that allows controllable synthesis of Cs1−xFAxPbI3 QDs across the whole composition range (x = 0–1), which is inaccessible in large-grain polycrystalline thin films. In an OA-rich environment, the cross-exchange of cations is facilitated, enabling rapid formation of Cs1−xFAxPbI3 QDs with reduced defect density. The hero Cs0.5FA0.5PbI3 QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that the QD devices exhibit substantially enhanced photostability compared with their thin-film counterparts because of suppressed phase segregation, and they retain 94% of the original PCE under continuous 1-sun illumination for 600 h.

Decoupling electrolytes towards stable and high-energy rechargeable aqueous zinc–manganese dioxide batteries

Abstract: Aqueous battery systems feature high safety, but they usually suffer from low voltage and low energy density, restricting their applications in large-scale storage. Here, we propose an electrolyte-decoupling strategy to maximize the full potential of Zn–MnO2 batteries by simultaneously enabling the optimal redox chemistry of both the Zn and MnO2 electrodes. The decoupled Zn–MnO2 battery exhibits an open-circuit voltage of 2.83 V (in contrast to the typical voltage of 1.5 V in conventional Zn–MnO2 batteries), as well as cyclability with only 2% capacity fading after deep cycling for 200 h. Benefiting from the full utilization of MnO2, the Zn–MnO2 battery is also able to maintain approximately 100% of its capacity at various discharge current densities. We also demonstrate the feasibility of integrating the Zn–MnO2 battery with a wind and photovoltaic hybrid power generating system. This electrolyte-decoupling strategy is shown to be applicable for other high-performance zinc-based aqueous batteries such as Zn–Cu and Zn–Ag batteries. Low energy density and limited cyclability are preventing the commercialization of aqueous Zn–MnO2 batteries. Here, the authors combine the merits of operating Zn anodes in alkaline conditions and MnO2 cathodes in acidic conditions, via an electrolyte-decoupling strategy, to realize high-performance batteries.

Tuning the interlayer spacing of graphene laminate films for efficient pore utilization towards compact capacitive energy storage

Abstract: Supercapacitors have shown extraordinary promise for miniaturized electronics and electric vehicles, but are usually limited by electrodes with rather low volumetric performance, which is largely due to the inefficient utilization of pores in charge storage. Herein, we design a freestanding graphene laminate film electrode with highly efficient pore utilization for compact capacitive energy storage. The interlayer spacing of this film can be precisely adjusted, which enables a tunable porosity. By systematically tailoring the pore size for the electrolyte ions, pores are utilized optimally and thereby the volumetric capacitance is maximized. Consequently, the fabricated supercapacitor delivers a stack volumetric energy density of 88.1 Wh l−1 in an ionic liquid electrolyte, representing a critical breakthrough for optimizing the porosity towards compact energy storage. Moreover, the optimized film electrode is assembled into an ionogel-based, all-solid-state, flexible smart device with multiple optional outputs and superior stability, demonstrating enormous potential as a portable power supply in practical applications. The volumetric performance of supercapacitors needs to be improved, but the usual trade-off between porosity and density is a problem. Here the authors develop a graphene laminate film with tunable porosity that leads to a volumetric energy density of 88.1 Wh l−1 at the device level.

The justice and equity implications of the clean energy transition

Abstract: The transition to lower-carbon sources of energy will inevitably produce and, in many cases, perpetuate pre-existing sets of winners and losers. The winners are those that will benefit from cleaner sources of energy, reduced emissions from the removal of fossil fuels, and the employment and innovation opportunities that accompany this transition. The losers are those that will bear the burdens, or lack access to the opportunities. Here we review the current state of understanding—based on a rapidly growing body of academic and policy literature—about the potential adverse consequences of the energy transition for specific communities and socio-economic groups on the frontlines of the transition. We review evidence about just transition policies and programmes, primarily from cases in the Global North, and draw conclusions about what insights are still needed to understand the justice and equity dimensions of the transition, and to ensure that no one is left behind. The costs and benefits of clean energy transitions will not be equally distributed. This Review of the literature on potential adverse impacts for specific communities highlights opportunities for future research to contribute to the design of policies and programmes that address these disparities.

The role of adsorbed hydroxide in hydrogen evolution reaction kinetics on modified platinum

Abstract: The bifunctional mechanism that involves adsorbed hydroxide in the alkaline hydrogen oxidation and evolution reactions, important in hydrogen fuel cells and water electrolysers, is hotly debated. Hydroxide binding has been suggested to impact activity, but the exact role of adsorbed hydroxide in the reaction mechanism is unknown. Here, by selectively decorating steps on a Pt single crystal with other metal atoms, we show that the rate of alkaline hydrogen evolution exhibits a volcano-type relationship with the hydroxide binding strength. We find that Pt decorated with Ru at the step edge is 65 times more active for the hydrogen evolution reaction (HER) than is the bare Pt step. Simulations of electrochemical water dissociation show that the activation energy correlates with the OH* adsorption strength, even when the adsorbed hydroxide is not a product, which leads to a simulated volcano curve that matches the experimental curve. This work not only illustrates the alkaline HER mechanism but also provides a goal for catalyst design in targeting an optimum hydroxide binding strength to yield the highest rate for the alkaline HER. A three-dimensional (H and OH adsorbed species) HER activity volcano and the implications for hydrogen oxidation are discussed. The appropriate descriptors for a catalyst’s hydrogen evolution activity in alkaline electrolyte are debated. Combining simulations and single-crystal studies of metal-decorated Pt surfaces, McCrum and Koper show that activity exhibits a volcano-type relationship with the hydroxide binding strength of the catalyst, providing a target for catalyst design.

The role of in situ generated morphological motifs and Cu(I) species in C2+ product selectivity during CO2 pulsed electroreduction

Abstract: The efficient electrochemical conversion of CO2 provides a route to fuels and feedstocks. Copper catalysts are well-known to be selective to multicarbon products, although the role played by the surface architecture and the presence of oxides is not fully understood. Here we report improved efficiency towards ethanol by tuning the morphology and oxidation state of the copper catalysts through pulsed CO2 electrolysis. We establish a correlation between the enhanced production of C2+ products (76% ethylene, ethanol and n-propanol at −1.0 V versus the reversible hydrogen electrode) and the presence of (100) terraces, Cu2O and defects on Cu(100). We monitored the evolution of the catalyst morphology by analysis of cyclic voltammetry curves and ex situ atomic force microscopy data, whereas the chemical state of the surface was examined via quasi in situ X-ray photoelectron spectroscopy. We show that the continuous regeneration of defects and Cu(i) species synergistically favours C–C coupling pathways. Carbon dioxide can be reduced electrocatalytically to fuels using copper catalysts, but the key features that determine the selectivity of these materials to specific products remains uncertain. Here Aran–Ais et al. use in situ methods to explore the influence of morphology and oxidation state on the performance of copper catalysts.

Molecular engineering of dispersed nickel phthalocyanines on carbon nanotubes for selective CO2 reduction

Abstract: Electrochemical reduction of CO2 is a promising route for sustainable production of fuels. A grand challenge is developing low-cost and efficient electrocatalysts that can enable rapid conversion with high product selectivity. Here we design a series of nickel phthalocyanine molecules supported on carbon nanotubes as molecularly dispersed electrocatalysts (MDEs), achieving CO2 reduction performances that are superior to aggregated molecular catalysts in terms of stability, activity and selectivity. The optimized MDE with methoxy group functionalization solves the stability issue of the original nickel phthalocyanine catalyst and catalyses the conversion of CO2 to CO with >99.5% selectivity at high current densities of up to −300 mA cm−2 in a gas diffusion electrode device with stable operation at −150 mA cm−2 for 40 h. The well-defined active sites of MDEs also facilitate the in-depth mechanistic understandings from in situ/operando X-ray absorption spectroscopy and theoretical calculations on structural factors that affect electrocatalytic performance. Widespread deployment of electrochemical CO2 reduction requires low-cost catalysts that perform well at high current densities. Zhang et al. show that methoxy-functionalized nickel phthalocyanine molecules on carbon nanotubes can operate as high-performing molecularly dispersed electrocatalysts at current densities of up to −300 mA cm–2.

Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation

Abstract: The carbon dioxide electroreduction reaction (CO2RR) provides ways to produce ethanol but its Faradaic efficiency could be further improved, especially in CO2RR studies reported at a total current density exceeding 10 mA cm−2. Here we report a class of catalysts that achieve an ethanol Faradaic efficiency of (52 ± 1)% and an ethanol cathodic energy efficiency of 31%. We exploit the fact that suppression of the deoxygenation of the intermediate HOCCH* to ethylene promotes ethanol production, and hence that confinement using capping layers having strong electron-donating ability on active catalysts promotes C–C coupling and increases the reaction energy of HOCCH* deoxygenation. Thus, we have developed an electrocatalyst with confined reaction volume by coating Cu catalysts with nitrogen-doped carbon. Spectroscopy suggests that the strong electron-donating ability and confinement of the nitrogen-doped carbon layers leads to the observed pronounced selectivity towards ethanol. The electroreduction of CO2 to ethanol could enable the clean production of fuels using renewable power. This study shows how confinement effects from nitrogen-doped carbon layers on copper catalysts enable selective ethanol production from CO2 with a Faradaic efficiency of up to 52%.

Highly quaternized polystyrene ionomers for high performance anion exchange membrane water electrolysers

Abstract: Alkaline anion exchange membrane (AEM) electrolysers to produce hydrogen from water are still at an early stage of development, and their performance is far lower than that of systems based on proton exchange membranes. Here, we report an ammonium-enriched anion exchange ionomer that improves the performance of an AEM electrolyser to levels approaching that of state-of-the-art proton exchange membrane electrolysers. Using rotating-disk electrode experiments, we show that a high pH (>13) in the electrode binder is the critical factor for improving the activity of the hydrogen- and oxygen-evolution reactions in AEM electrolysers. Based on this observation, we prepared and tested several quaternized polystyrene electrode binders in an AEM electrolyser. Using the binder with the highest ionic concentration and a NiFe oxygen evolution catalyst, we demonstrated performance of 2.7 A cm−2 at 1.8 V without a corrosive circulating alkaline solution. The limited durability of the AEM electrolyser remains a challenge to be addressed in the future. Anion exchange membrane water electrolysers have potential cost advantages over proton exchange membrane electrolysers, but their performance has lagged behind. Here the authors investigate the cause of the poor performance of anion exchange membrane electrolysers and design ionomers that can overcome some of the challenges.

Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper

Abstract: Direct electrochemical conversion of CO2 to ethanol offers a promising strategy to lower CO2 emissions while storing energy from renewable electricity. However, current electrocatalysts offer only limited selectivity toward ethanol. Here we report a carbon-supported copper (Cu) catalyst, synthesized by an amalgamated Cu–Li method, that achieves a single-product Faradaic efficiency (FE) of 91% at −0.7 V (versus the reversible hydrogen electrode) and onset potential as low as −0.4 V (reversible hydrogen electrode) for electrocatalytic CO2-to-ethanol conversion. The catalyst operated stably over 16 h. The FE of ethanol was highly sensitive to the initial dispersion of Cu atoms and decreased significantly when CuO and large Cu clusters become predominant species. Operando X-ray absorption spectroscopy identified a reversible transformation from atomically dispersed Cu atoms to Cun clusters (n = 3 and 4) on application of electrochemical conditions. First-principles calculations further elucidate the possible catalytic mechanism of CO2 reduction over Cun. Electrocatalytically reducing CO2 to ethanol can provide renewably generated fuel, but catalysts are often poorly selective for this conversion. Here the authors use a Cu catalyst to produce ethanol with high selectivity. Cu dispersion is key to the performance and operando studies indicate that it changes under reaction conditions.

Hydrothermal deposition of antimony selenosulfide thin films enables solar cells with 10% efficiency

Abstract: Antimony selenosulfide, Sb2(S,Se)3, has attracted attention over the last few years as a light-harvesting material for photovoltaic technology owing to its phase stability, earth abundancy and low toxicity. However, the lack of a suitable material processing approach to obtain Sb2(S,Se)3 films with optimal optoelectronic properties and morphology severely hampers prospects for efficiency improvement. Here we demonstrate a hydrothermal approach to deposit high-quality Sb2(S,Se)3 films. By varying the Se/S ratio and the temperature of the post-deposition annealing, we improve the film morphology, increase the grain size and reduce the number of defects. In particular, we find that increasing the Se/S ratio leads to a favourable orientation of the (Sb4S(e)6)n ribbons (S(e) represents S or Se). By optmizing the hydrothermal deposition parameters and subsequent annealing, we report a Sb2(S,Se)3 cell with a certified 10.0% efficiency. This result highlights the potential of Sb2(S,Se)3 as an emerging photovoltaic material. Antimony chalcogenides are emerging photovoltaic materials, yet difficulties in fabricating high-quality films limit device performance. We show that hydrothermal synthesis affords good morphology and reduced defects in antimony selenosulfide films, enabling solar cells with an efficiency of 10%.

Quantifying the impacts of climate change and extreme climate events on energy systems

Abstract: Climate induced extreme weather events and weather variations will affect both the demand of energy and the resilience of energy supply systems. The specific potential impact of extreme events on energy systems has been difficult to quantify due to the unpredictability of future weather events. Here we develop a stochastic-robust optimization method to consider both low impact variations and extreme events. Applications of the method to 30 cities in Sweden, by considering 13 climate change scenarios, reveal that uncertainties in renewable energy potential and demand can lead to a significant performance gap (up to 34% for grid integration) brought by future climate variations and a drop in power supply reliability (up to 16%) due to extreme weather events. Appropriate quantification of the climate change impacts will ensure robust operation of the energy systems and enable renewable energy penetration above 30% for a majority of the cities.

Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis

Abstract: Anode-free lithium metal cells store 60% more energy per volume than conventional lithium-ion cells. Such high energy density can increase the range of electric vehicles by approximately 280 km or even enable electrified urban aviation. However, these cells tend to experience rapid capacity loss and short cycle life. Furthermore, safety issues concerning metallic lithium often remain unaddressed in the literature. Recently, we demonstrated long-lifetime anode-free cells using a dual-salt carbonate electrolyte. Here we characterize the degradation of anode-free cells with this lean (2.6 g Ah−1) liquid electrolyte. We observe deterioration of the pristine lithium morphology using scanning electron microscopy and X-ray tomography, and diagnose the cause as electrolyte degradation and depletion using nuclear magnetic resonance spectroscopy and ultrasonic transmission mapping. For the safety characterization tests, we measure the cell temperature during nail penetration. Finally, we use the insights gained in this work to develop an optimized electrolyte, extending the lifetime of anode-free cells to 200 cycles. Anode-free batteries have emerged as a promising storage means to offer high energy density but still suffer from long-term reversibility. The authors analyse the cell failure mechanisms and present an optimized electrolyte to extend the lifetime of anode-free pouch cells.