Showing papers on "Overpotential published in 2017"
TL;DR: The Ru@C2N electrocatalyst, made of Ru nanoparticles dispersed within a nitrogenated holey two-dimensional carbon structure, exhibits high turnover frequencies and superior stability in both acidic and alkaline media, comparable to, or even better than, the Pt/C catalyst for the HER.
Abstract: Ruthenium nanoparticles homogeneously dispersed in a nitrogenated, two-dimensional carbon matrix show high turnover frequency and small overpotential for hydrogen evolution reaction both in acidic and alkaline media. The hydrogen evolution reaction (HER) is a crucial step in electrochemical water splitting and demands an efficient, durable and cheap catalyst if it is to succeed in real applications1,2,3. For an energy-efficient HER, a catalyst must be able to trigger proton reduction with minimal overpotential4 and have fast kinetics5,6,7,8,9. The most efficient catalysts in acidic media are platinum-based, as the strength of the Pt–H bond10 is associated with the fastest reaction rate for the HER11,12. The use of platinum, however, raises issues linked to cost and stability in non-acidic media. Recently, non-precious-metal-based catalysts have been reported, but these are susceptible to acid corrosion and are typically much inferior to Pt-based catalysts, exhibiting higher overpotentials and lower stability13,14,15. As a cheaper alternative to platinum, ruthenium possesses a similar bond strength with hydrogen (∼65 kcal mol–1)16, but has never been studied as a viable alternative for a HER catalyst. Here, we report a Ru-based catalyst for the HER that can operate both in acidic and alkaline media. Our catalyst is made of Ru nanoparticles dispersed within a nitrogenated holey two-dimensional carbon structure (Ru@C2N). The Ru@C2N electrocatalyst exhibits high turnover frequencies at 25 mV (0.67 H2 s−1 in 0.5 M H2SO4 solution; 0.75 H2 s−1 in 1.0 M KOH solution) and small overpotentials at 10 mA cm–2 (13.5 mV in 0.5 M H2SO4 solution; 17.0 mV in 1.0 M KOH solution) as well as superior stability in both acidic and alkaline media. These performances are comparable to, or even better than, the Pt/C catalyst for the HER.
1,105 citations
TL;DR: A facile solution reduction method using NaBH4 as a reductant is developed to prepare iron-cobalt oxide nanosheets (Fex Coy -ONSs) with a large specific surface area, ultrathin thickness, and, importantly, abundant oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H2 O onto nearby Co3+ sites.
Abstract: Electrochemical water splitting is a promising method for storing light/electrical energy in the form of H2 fuel; however, it is limited by the sluggish anodic oxygen evolution reaction (OER). To improve the accessibility of H2 production, it is necessary to develop an efficient OER catalyst with large surface area, abundant active sites, and good stability, through a low-cost fabrication route. Herein, a facile solution reduction method using NaBH4 as a reductant is developed to prepare iron-cobalt oxide nanosheets (FexCoy-ONSs) with a large specific surface area (up to 261.1 m2 g−1), ultrathin thickness (1.2 nm), and, importantly, abundant oxygen vacancies. The mass activity of Fe1Co1-ONS measured at an overpotential of 350 mV reaches up to 54.9 A g−1, while its Tafel slope is 36.8 mV dec−1; both of which are superior to those of commercial RuO2, crystalline Fe1Co1-ONP, and most reported OER catalysts. The excellent OER catalytic activity of Fe1Co1-ONS can be attributed to its specific structure, e.g., ultrathin nanosheets that could facilitate mass diffusion/transport of OH− ions and provide more active sites for OER catalysis, and oxygen vacancies that could improve electronic conductivity and facilitate adsorption of H2O onto nearby Co3+ sites.
1,058 citations
TL;DR: This work adopts metal-organic frameworks (MOFs) to assist the preparation of a catalyst containing single Ni sites for efficient electroreduction of CO2 and presents some guidelines for the rational design and accurate modulation of nanostructured catalysts at the atomic scale.
Abstract: Single-atom catalysts often exhibit unexpected catalytic activity for many important chemical reactions because of their unique electronic and geometric structures with respect to their bulk counterparts. Herein we adopt metal–organic frameworks (MOFs) to assist the preparation of a catalyst containing single Ni sites for efficient electroreduction of CO2. The synthesis is based on ionic exchange between Zn nodes and adsorbed Ni ions within the cavities of the MOF. This single-atom catalyst exhibited an excellent turnover frequency for electroreduction of CO2 (5273 h–1), with a Faradaic efficiency for CO production of over 71.9% and a current density of 10.48 mA cm–2 at an overpotential of 0.89 V. Our findings present some guidelines for the rational design and accurate modulation of nanostructured catalysts at the atomic scale.
1,005 citations
TL;DR: This work fabricates a nickel-iron-based metal-organic framework array, which demonstrates superior electrocatalytic performance towards oxygen evolution reaction with a small overpotential, and robust operation for 20,000s with no detectable activity decay, and demonstrates the promise of these electrodes for other important catalytic reactions including hydrogen evolution reaction and overall water splitting.
Abstract: Two-dimensional metal-organic frameworks represent a family of materials with attractive chemical and structural properties, which are usually prepared in the form of bulk powders. Here we show a generic approach to fabricate ultrathin nanosheet array of metal-organic frameworks on different substrates through a dissolution–crystallization mechanism. These materials exhibit intriguing properties for electrocatalysis including highly exposed active molecular metal sites owning to ultra-small thickness of nanosheets, improved electrical conductivity and a combination of hierarchical porosity. We fabricate a nickel-iron-based metal-organic framework array, which demonstrates superior electrocatalytic performance towards oxygen evolution reaction with a small overpotential of 240 mV at 10 mA cm−2, and robust operation for 20,000 s with no detectable activity decay. Remarkably, the turnover frequency of the electrode is 3.8 s−1 at an overpotential of 400 mV. We further demonstrate the promise of these electrodes for other important catalytic reactions including hydrogen evolution reaction and overall water splitting. Metal-organic frameworks are generally considered to be inert catalysts for many electrochemical reactions, however this is not always the case. Here the authors fabricate an ultrathin nanosheet array of metal-organic frameworks exhibiting enhanced performance toward electrocatalytic water splitting.
968 citations
TL;DR: In this paper, LiPF6 was used as an additive in LiTFSI-LiBOB dual-salt/carbonate-solvent-based electrolytes to enhance the charging capability and cycling stability of Li metal batteries.
Abstract: Batteries using lithium (Li) metal as anodes are considered promising energy storage systems because of their high energy densities. However, safety concerns associated with dendrite growth along with limited cycle life, especially at high charge current densities, hinder their practical uses. Here we report that an optimal amount (0.05 M) of LiPF6 as an additive in LiTFSI–LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. In a Li metal battery using a 4-V Li-ion cathode at a moderately high loading of 1.75 mAh cm−2, a cyclability of 97.1% capacity retention after 500 cycles along with very limited increase in electrode overpotential is accomplished at a charge/discharge current density up to 1.75 mA cm−2. The fast charging and stable cycling performances are ascribed to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector. Deployment of rechargeable Li metal batteries requires fast charging capability and long-term cycling stability. Here the authors demonstrate the battery application potential of using a small amount of LiPF6 in a dual-salt electrolyte.
955 citations
TL;DR: It is demonstrated that the Li2S decomposition energy barrier is associated with the binding between isolated Li ions and the sulfur in sulfides; this is the main reason that sulfide materials can induce lower overpotential compared with commonly used carbon materials.
Abstract: Polysulfide binding and trapping to prevent dissolution into the electrolyte by a variety of materials has been well studied in Li−S batteries. Here we discover that some of those materials can play an important role as an activation catalyst to facilitate oxidation of the discharge product, Li2S, back to the charge product, sulfur. Combining theoretical calculations and experimental design, we select a series of metal sulfides as a model system to identify the key parameters in determining the energy barrier for Li2S oxidation and polysulfide adsorption. We demonstrate that the Li2S decomposition energy barrier is associated with the binding between isolated Li ions and the sulfur in sulfides; this is the main reason that sulfide materials can induce lower overpotential compared with commonly used carbon materials. Fundamental understanding of this reaction process is a crucial step toward rational design and screening of materials to achieve high reversible capacity and long cycle life in Li−S batteries.
933 citations
TL;DR: The computations revealed that the single Mo atom supported by a defective BN nanosheet exhibits the highest catalytic activity for N2 fixation at room temperature through an enzymatic mechanism with a quite low overpotential of 0.19 V.
Abstract: The production of ammonia (NH3) from molecular dinitrogen (N2) under mild conditions is one of the most attractive and challenging processes in chemistry. Here by means of density functional theory (DFT) computations, we systematically investigated the potential of single transition metal atoms (Sc to Zn, Mo, Ru, Rh, Pd, and Ag) supported on the experimentally available defective boron nitride (TM–BN) monolayer with a boron monovacancy as a N2 fixation electrocatalyst. Our computations revealed that the single Mo atom supported by a defective BN nanosheet exhibits the highest catalytic activity for N2 fixation at room temperature through an enzymatic mechanism with a quite low overpotential of 0.19 V. The high spin-polarization, selective stabilization of N2H* species, or destabilizing NH2* species are responsible for the high activity of the Mo-embedded BN nanosheet for N2 fixation. This finding opens a new avenue of NH3 production by single-atom electrocatalysts under ambient conditions.
920 citations
TL;DR: A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time, exhibiting higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions.
Abstract: Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.
898 citations
TL;DR: The authors demonstrate a heterostructured NiFe LDH-NS@DG10 hybrid catalyst by coupling of exfoliated Ni-Fe layered double hydroxide (LDH) nanosheet (NS) and defective graphene (DG).
Abstract: Herein, the authors demonstrate a heterostructured NiFe LDH-NS@DG10 hybrid catalyst by coupling of exfoliated Ni-Fe layered double hydroxide (LDH) nanosheet (NS) and defective graphene (DG). The catalyst has exhibited extremely high electrocatalytic activity for oxygen evolution reaction (OER) in an alkaline solution with an overpotential of 0.21 V at a current density of 10 mA cm-2, which is comparable to the current record (≈0.20 V in Fe-Co-Ni metal-oxide-film system) and superior to all other non-noble metal catalysts. Also, it possesses outstanding kinetics (Tafel slope of 52 mV dec-1) for the reaction. Interestingly, the NiFe LDH-NS@DG10 hybrid has also exhibited the high hydrogen evolution reaction (HER) performance in an alkaline solution (with an overpotential of 115 mV by 2 mg cm-2 loading at a current density of 20 mA cm-2) in contrast to barely HER activity for NiFe LDH-NS itself. As a result, the bifunctional catalyst the authors developed can achieve a current density of 20 mA cm-2 by a voltage of only 1.5 V, which is also a record for the overall water splitting. Density functional theory calculation reveals that the synergetic effects of highly exposed 3d transition metal atoms and carbon defects are essential for the bifunctional activity for OER and HER
794 citations
TL;DR: Benefiting from its scalable preparation and stability, the MoNi4 electrocatalyst is promising for practical water-alkali electrolysers and comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts.
Abstract: Various platinum-free electrocatalysts have been explored for hydrogen evolution reaction in acidic solutions. However, in economical water-alkali electrolysers, sluggish water dissociation kinetics (Volmer step) on platinum-free electrocatalysts results in poor hydrogen-production activities. Here we report a MoNi4 electrocatalyst supported by MoO2 cuboids on nickel foam (MoNi4/MoO2@Ni), which is constructed by controlling the outward diffusion of nickel atoms on annealing precursor NiMoO4 cuboids on nickel foam. Experimental and theoretical results confirm that a rapid Tafel-step-decided hydrogen evolution proceeds on MoNi4 electrocatalyst. As a result, the MoNi4 electrocatalyst exhibits zero onset overpotential, an overpotential of 15 mV at 10 mA cm-2 and a low Tafel slope of 30 mV per decade in 1 M potassium hydroxide electrolyte, which are comparable to the results for platinum and superior to those for state-of-the-art platinum-free electrocatalysts. Benefiting from its scalable preparation and stability, the MoNi4 electrocatalyst is promising for practical water-alkali electrolysers.
785 citations
TL;DR: It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity.
Abstract: Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and...
TL;DR: Porous CoFe2 O4 /C NRAs supported on nickel foam@NC are directly fabricated by the carbonization of bimetal-organic framework NRAs grown on NF@poly-aniline(PANI), and they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.
Abstract: Porous CoFe2 O4 /C NRAs supported on nickel foam@NC (denoted as NF@NC-CoFe2 O4 /C NRAs) are directly fabricated by the carbonization of bimetal-organic framework NRAs grown on NF@poly-aniline(PANI), and they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.
TL;DR: It is found that zinc-doped MoS2 (Zn-MoS2) exhibits superior electrochemical activity toward HER as evidenced by the positively shifted onset potential to -0.13 V vs RHE.
Abstract: Water-splitting devices for hydrogen generation through electrolysis (hydrogen evolution reaction, HER) hold great promise for clean energy. However, their practical application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. We previously reported that HER can be largely enhanced through finely tuning the energy level of molybdenum sulfide (MoS2) by hot electron injection from plasmonic gold nanoparticles. Under this inspiration, herein, we propose a strategy to improve the HER performance of MoS2 by engineering its energy level via direct transition-metal doping. We find that zinc-doped MoS2 (Zn-MoS2) exhibits superior electrochemical activity toward HER as evidenced by the positively shifted onset potential to -0.13 V vs RHE. A turnover of 15.44 s-1 at 300 mV overpotential is achieved, which by far exceeds the activity of MoS2 catalysts reported. The large enhancement can be attributed to the synergistic effect of electronic effect (energy level matching) and morphological effect (rich active sites) via thermodynamic and kinetic acceleration, respectively. This design opens up further opportunities for improving electrocatalysts by incorporating promoters, which broadens the understanding toward the optimization of electrocatalytic activity of these unique materials.
TL;DR: In this article, the authors demonstrate that when using a Li metal electrode, the dynamic changes in voltage during extended cycles can be increasingly attributed to mass transport, which introduces a tortuous pathway for Li-ion transport.
Abstract: Improvement of the performance of Li metal anodes is critical to enable high energy density rechargeable battery systems beyond Li-ion. However, a complete mechanistic understanding of electrode overpotential variations that occur during extended cycling of Li metal is lacking. Herein, we demonstrate that when using a Li metal electrode, the dynamic changes in voltage during extended cycles can be increasingly attributed to mass transport. It is shown that these mass transport effects arise as a result of dead Li accumulation at the Li metal electrode, which introduces a tortuous pathway for Li-ion transport. In Li–Li symmetric cells, mass transport effects cause the shape of the galvanostatic voltage response to change from “peaking” to “arcing”, along with an increase in total electrode overpotential. The continued accumulation of dead Li is also conclusively shown to directly cause capacity fade and rapid “failure” of Li–LCO full cells containing Li metal anodes. This work provides detailed insights into the coupled relationships between cycling, interphase morphology, mass transport and the overall cell performance. Furthermore, this work helps underscore the potential of Li–Li symmetric cells as a powerful analytical tool for understanding the effects of Li metal electrodes in full cell batteries.
TL;DR: The first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared and has a higher specific surface area and an increased number of active sites for OER and ORR.
Abstract: Metal-free electrocatalysts have been extensively developed to replace noble metal Pt and RuO2 catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal-air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma-etched carbon cloth (P-CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P-CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P-CC has a low overpotential that is comparable to Pt-based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.
TL;DR: A cobalt-phthalocyanine-based high-performance carbon dioxide reduction electrocatalyst material developed with a combined nanoscale and molecular approach that exhibits >95% Faradaic efficiency for carbon monoxide production in a wide potential range and extraordinary catalytic activity.
Abstract: Electrochemical reduction of carbon dioxide with renewable energy is a sustainable way of producing carbon-neutral fuels. However, developing active, selective and stable electrocatalysts is challenging and entails material structure design and tailoring across a range of length scales. Here we report a cobalt-phthalocyanine-based high-performance carbon dioxide reduction electrocatalyst material developed with a combined nanoscale and molecular approach. On the nanoscale, cobalt phthalocyanine (CoPc) molecules are uniformly anchored on carbon nanotubes to afford substantially increased current density, improved selectivity for carbon monoxide, and enhanced durability. On the molecular level, the catalytic performance is further enhanced by introducing cyano groups to the CoPc molecule. The resulting hybrid catalyst exhibits >95% Faradaic efficiency for carbon monoxide production in a wide potential range and extraordinary catalytic activity with a current density of 15.0 mA cm−2 and a turnover frequency of 4.1 s−1 at the overpotential of 0.52 V in a near-neutral aqueous solution. Electrochemical reduction of carbon dioxide is a sustainable way of producing carbon-neutral fuels. Here, the authors take a combined nanoscale and molecular approach to develop a highly active and selective cobalt phthalocyanine/carbon nanotube hybrid electrocatalyst for carbon dioxide reduction to carbon monoxide.
TL;DR: In this article, a cobalt molybdenum phosphide nanocrystal coated by a few-layer N-doped carbon shell (CoMoP@C) is used for hydrogen evolution reaction.
Abstract: The hydrogen evolution reaction (HER) based on water electrolysis is a promising strategy for hydrogen energy production, in which the key point is seeking low-cost, high efficiency and stable electrocatalysts. Currently, the most efficient electrocatalysts for the HER are Pt-based catalysts (especially commercial Pt/C), but the low abundance and high cost of Pt hinder their widespread application. Herein, we demonstrate that a cobalt molybdenum phosphide nanocrystal coated by a few-layer N-doped carbon shell (CoMoP@C) is an excellent substitute for the HER. CoMoP@C is prepared by a one-step pyrolysis method on a large scale with polyoxometalate (POM) as a molecular platform. The catalytic activity of CoMoP@C is close to that of commercial 20% Pt/C under pH = 0–1 conditions and superior to that of 20% Pt/C under pH = 2–14 conditions at high overpotential (e.g. η > 240 mV at pH = 2.2). In real seawater, CoMoP@C exhibits stable HER performance with a high Faradaic efficiency (FE) of 92.5%, while the HER activity of 20% Pt/C dramatically decreases after 4 h. The remarkable HER performance of CoMoP@C should be attributed to the low free energy of H on the central CoMoP crystalline core and the multiple functions of the outer N-doped C shell (especially the strong H+ absorption behavior). This work may provide new options for the design and preparation of promising HER electrocatalysts superior to Pt/C, which can be used directly in seawater.
TL;DR: In this paper, three categories of non-noble metal electrocatalysts are under heavy investigations: (i) alloys, (ii) transition metal compounds, and (iii) carbonaceous nanomaterials.
TL;DR: A 3D hierarchical structure composed of mesoporous SnO2 nanosheets on carbon cloth is proposed to efficiently and selectively electroreduce CO2 to formate in aqueous media and demonstrates flexibility and long-term stability.
Abstract: Electrochemical reduction of CO2 into liquid fuels is a promising approach to achieve a carbon-neutral energy cycle. However, conventional electrocatalysts usually suffer from low energy efficiency and poor selectivity and stability. A 3D hierarchical structure composed of mesoporous SnO2 nanosheets on carbon cloth is proposed to efficiently and selectively electroreduce CO2 to formate in aqueous media. The electrode is fabricated by a facile combination of hydrothermal reaction and calcination. It exhibits an unprecedented partial current density of about 45 mA cm−2 at a moderate overpotential (0.88 V) with high faradaic efficiency (87±2 %), which is even larger than most gas diffusion electrodes. Additionally, the electrode also demonstrates flexibility and long-term stability. The superior performance is attributed to the robust and highly porous hierarchical structure, which provides a large surface area and facilitates charge and mass transfer.
TL;DR: A new way for designing oxygen vacancies dominated interface nanowires as highly efficient multifunctional electrocatalysts for electrochemical reactions and renewable energy devices is opened.
Abstract: The development of highly active and stable oxygen evolution reaction (OER) electrocatalysts is crucial for improving the efficiency of water splitting and metal-air battery devices. Herein, an efficient strategy is demonstrated for making the oxygen vacancies dominated cobalt-nickel sulfide interface porous nanowires (NiS2 /CoS2 -O NWs) for boosting OER catalysis through in situ electrochemical reaction of NiS2 /CoS2 interface NWs. Because of the abundant oxygen vacancies and interface porous nanowires structure, they can catalyze the OER efficiently with a low overpotential of 235 mV at j = 10 mA cm-2 and remarkable long-term stability in 1.0 m KOH. The home-made rechargeable portable Zn-air batteries by using NiS2 /CoS2 -O NWs as the air-cathode display a very high open-circuit voltage of 1.49 V, which can maintain for more than 30 h. Most importantly, a highly efficient self-driven water splitting device is designed with NiS2 /CoS2 -O NWs as both anode and cathode, powered by two-series-connected NiS2 /CoS2 -O NWs-based portable Zn-air batteries. The present work opens a new way for designing oxygen vacancies dominated interface nanowires as highly efficient multifunctional electrocatalysts for electrochemical reactions and renewable energy devices.
TL;DR: It is shown that ultrafine silver (Ag) nanoparticles, which are synthesized via a novel rapid Joule heating method, can serve as nanoseeds to direct the deposition of Li within the 3D host materials, resolving the problems of the Li metal anode.
Abstract: To exploit the high energy density of the lithium (Li) metal battery, it is imperative to address the dendrite growth and interface instability of the anode. 3D hosts for Li metal are expected to suppress the growth of Li dendrites. Heterogeneous seeds are effective in guiding Li deposition and realizing spatial control over Li nucleation. Herein, this study shows that ultrafine silver (Ag) nanoparticles, which are synthesized via a novel rapid Joule heating method, can serve as nanoseeds to direct the deposition of Li within the 3D host materials, resolving the problems of the Li metal anode. By optimizing the Joule heating method, ultrafine Ag nanoparticles (≈40 nm) are homogeneously anchored on carbon nanofibers. The Ag nanoseeds effectively reduce the nucleation overpotential of Li and guide the Li deposition in the 3D carbon matrix uniformly, free from the dendrites. A stable and reversible Li metal anode is achieved in virtue of the Ag nanoseeds in the 3D substrate, showing a low overpotential (≈0.025 V) for a long cycle life. The ultrafine nanoseeds achieved by rapid Joule heating render uniform deposition of Li metal anode in 3D hosts, promising a safe and long-life Li metal battery for high-energy applications.
TL;DR: Density functional theory calculations reveal that the significantly enhanced electrocatalytic activity and selectivity at lowered overpotential originate from the shape-controlled structure, which provides the optimum edge-to-corner ratio and dominates at the facet of Ag(100) where it requires lower energy to initiate the rate-determining step.
Abstract: Electrochemical reduction of CO2 (CO2RR) provides great potential for intermittent renewable energy storage. This study demonstrates a predominant shape-dependent electrocatalytic reduction of CO2 to CO on triangular silver nanoplates (Tri-Ag-NPs) in 0.1 M KHCO3. Compared with similarly sized Ag nanoparticles (SS-Ag-NPs) and bulk Ag, Tri-Ag-NPs exhibited an enhanced current density and significantly improved Faradaic efficiency (96.8%) and energy efficiency (61.7%), together with a considerable durability (7 days). Additionally, CO starts to be observed at an ultralow overpotential of 96 mV, further confirming the superiority of Tri-Ag-NPs as a catalyst for CO2RR toward CO formation. Density functional theory calculations reveal that the significantly enhanced electrocatalytic activity and selectivity at lowered overpotential originate from the shape-controlled structure. This not only provides the optimum edge-to-corner ratio but also dominates at the facet of Ag(100) where it requires lower energy to in...
TL;DR: It is shown that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction, in contrast to the disordered alloy NP.
Abstract: Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced ca...
TL;DR: In this paper, 3D self-supported Fe-doped Ni2P nanosheet arrays are synthesized on Ni foam by hydrothermal method followed by in situ phosphorization, which serve as bifunctional electrocatalysts for overall water splitting.
Abstract: The development of highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for improving the efficiency of overall water splitting, but still remains challenging issue. Herein, 3D self-supported Fe-doped Ni2P nanosheet arrays are synthesized on Ni foam by hydrothermal method followed by in situ phosphorization, which serve as bifunctional electrocatalysts for overall water splitting. The as-synthesized (Ni0.33Fe0.67)2P with moderate Fe doping shows an outstanding OER performance, which only requires an overpotential of ≈230 mV to reach 50 mA cm−2 and is more efficient than the other Fe incorporated Ni2P electrodes. In addition, the (Ni0.33Fe0.67)2P exhibits excellent activity toward HER with a small overpotential of ≈214 mV to reach 50 mA cm−2. Furthermore, an alkaline electrolyzer is measured using (Ni0.33Fe0.67)2P electrodes as cathode and anode, respectively, which requires cell voltage of 1.49 V to reach 10 mA cm−2 as well as shows excellent stability with good nanoarray construction. Such good performance is attributed to the high intrinsic activity and superaerophobic surface property.
TL;DR: In this article, a Cu, Co-embedded nitrogen-enriched mesoporous carbon framework (CuCo@NC) is developed using, a facile Cu-confined thermal conversion strategy of zeolitic imidazolate frameworks (ZIF-67) pre-grown on Cu(OH)2 nanowires.
Abstract: Rational synthesis of hybrid, earth-abundant materials with efficient electrocatalytic functionalities are critical for sustainable energy applications. Copper is theoretically proposed to exhibit high reduction capability close to Pt, but its high diffusion behavior at elevated fabrication temperatures limits its homogeneous incorporation with carbon. Here, a Cu, Co-embedded nitrogen-enriched mesoporous carbon framework (CuCo@NC) is developed using, a facile Cu-confined thermal conversion strategy of zeolitic imidazolate frameworks (ZIF-67) pre-grown on Cu(OH)2 nanowires. Cu ions formed below 450 °C are homogeneously confined within the pores of ZIF-67 to avoid self-aggregation, while the existence of CuN bonds further increases the nitrogen content in carbon frameworks derived from ZIF-67 at higher pyrolysis temperatures. This CuCo@NC electrocatalyst provides abundant active sites, high nitrogen doping, strong synergetic coupling, and improved mass transfer, thus significantly boosting electrocatalytic performances in oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). A high half-wave potential (0.884 V vs reversible hydrogen potential, RHE) and a large diffusion-limited current density are achieved for ORR, comparable to or exceeding the best reported earth-abundant ORR electrocatalysts. In addition, a low overpotential (145 mV vs RHE) at 10 mA cm−2 is demonstrated for HER, further suggesting its great potential as an efficient electrocatalyst for sustainable energy applications.
TL;DR: In this paper, the authors reported the development of Mn-doped CoP (Mn-Co-P/Ti) nanosheets array on Ti mesh as an efficient 3D HER electrocatalyst with good stability.
Abstract: Heteratom doping is a possible way to tune the hydrogen evolution reaction (HER) catalytic capability of electrocatalysts. In this work, we report the development of Mn-doped CoP (Mn–Co–P) nanosheets array on Ti mesh (Mn–Co–P/Ti) as an efficient 3D HER electrocatalyst with good stability at all pH values. Electrochemical tests demonstrate that Mn doping leads to enhanced catalytic activity of CoP. In 0.5 M H2SO4, this Mn–Co–P/Ti catalyst drives 10 mA cm–2 at an overpotential of 49 mV, which is 32 mV less than that for CoP/Ti. To achieve the same current density, it demands overpotentials of 76 and 86 mV in 1.0 M KOH and phosphate-buffered saline, respectively. The enhanced HER activity for Mn–Co–P can be attributed to its more thermo-neutral hydrogen adsorption free energy than CoP, which is supported by density functional theory calculations.
TL;DR: In this paper, the authors describe the recent progress on engineering the electrode-electrolyte and semiconductor-cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency.
Abstract: The efficiency of photoelectrocatalytic (PEC) water splitting is limited by the serious recombination of photogenerated charges, high overpotential, and sluggish kinetics of surface reaction. Herein we describe the recent progress on engineering the electrode–electrolyte and semiconductor–cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency. Introducing cocatalysts has been demonstrated to be the most efficient way to lower the reaction barrier and promote charge injection to the reactants. In addition, it has been found that electrolyte ions can influence the surface catalysis remarkably. Electrolyte cations on the surface can influence the water splitting and backward reactions, and anions may take part in the proton transfer processes, indicating that fine-tuning of the electrolyte parameters turns out to be an important strategy for enhancing the PEC efficiency. Moreover, careful modification of the interface between the cocatalysts ...
TL;DR: Extended X-ray absorption fine structure analysis combined with electrochemical test shows that carbon shell coating prevents FeP nanoparticles from oxidation, making them highly stable under hydrogen evolution reaction operation conditions.
Abstract: A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm–2, which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extende...
TL;DR: In this article, a ternary NiCoP/carbon cloth (CC) electrocatalyst with superior catalytic activity and stability for hydrogen evolution reaction and oxygen evolution reaction was proposed.
Abstract: The investigation of high-efficiency nonprecious electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great significance for renewable energy technologies. Here, we provide a successive hydrothermal, oxidation, and phosphidation method to fabricate a 3D nest-like ternary NiCoP/carbon cloth (CC) electrocatalyst with superior catalytic activity and stability toward HER/OER. Nest-like NiCoP/CC requires overpotentials of 44 and 62 mV to reach the current density of 10 mA cm–2 in acidic and alkaline media, respectively, toward HER. For OER, the NiCoP/CC exhibits high active and durable performance with an overpotential of 242 mV at current density of 10 mA cm–2 in alkaline solutions. Furthermore, the practical application of NiCoP/CC as a bifunctional catalyst for overall water splitting reaction yields current densities of 10 and 100 mA cm–2 at 1.52 and 1.77 V, respectively.
TL;DR: An overpotential of 540 mV at 10 mA cm-2 is attained in an acidic electrolyte and stable for over 30 h, which is the best OER performance in both alkaline and acidic media.
Abstract: The intrinsic catalytic activity at 10 mA cm-2 for oxygen evolution reaction (OER) is currently working out at overpotentials higher than 320 mV. A highly efficient electrocatalyst should possess both active sites and high conductivity; however, the loading of powder catalysts on electrodes may often suffer from the large resistance between catalysts and current collectors. This work reports a class of bulk amorphous NiFeP materials with metallic bonds from the viewpoint of electrode design. The materials reported here perfectly combine high macroscopic conductivity with surface active sites, and can be directly used as the electrodes with active sites toward high OER activity in both alkaline and acidic electrolytes. Specifically, a low overpotential of 219 mV is achieved at the geometric current density 10 mA cm-2 in an alkaline electrolyte, with the Tafel slope of 32 mV dec-1 and intrinsic overpotential of 280 mV. Meanwhile, an overpotential of 540 mV at 10 mA cm-2 is attained in an acidic electrolyte and stable for over 30 h, which is the best OER performance in both alkaline and acidic media. This work provides a different angle for the design of high-performance OER electrocatalysts and facilitates the device applications of electrocatalysts.