Showing papers on "Catalysis published in 2021"

Electrochemical ammonia synthesis via nitrate reduction on Fe single atom catalyst.

Abstract: Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h−1 mgcat.−1 (0.46 mmol h−1 cm−2). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N2 due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites. Developing green and delocalized routes for ammonia synthesis is highly important but still very challenging. Here the authors report an efficient ammonia synthesis process via nitrate reduction to ammonia on Fe single atom catalyst.

Regulating Fe-spin state by atomically dispersed Mn-N in Fe-N-C catalysts with high oxygen reduction activity.

Abstract: As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4 /C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen. Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. The work brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts. The working mechanism of several low-cost electrocatalyst materials is still arguable. Here the authors show a model Fe,Mn/N-C catalyst where the oxygen reduction preferentially takes place on Fe(III) sites with the intermediate spin state (t2g4 eg1) caused by the adjacent Mn-N moieties.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activation of Peroxymonosulfate to Generate 1O2 with 100 % Selectivity

Abstract: Singlet oxygen (1 O2 ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of 1 O2 . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe1 /CN) containing highly uniform Fe-N4 active sites with a high Fe loading of 11.2 wt %. The Fe1 /CN achieves generation of 100 % 1 O2 by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N4 sites in Fe1 /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO5 .- , and thereafter efficiently generate 1 O2 with 100 % selectivity. In addition, the Fe1 /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of 1 O2 for highly selective and efficient degradation of pollutants.

High efficiency heterogeneous Fenton-like catalyst biochar modified CuFeO2 for the degradation of tetracycline: Economical synthesis, catalytic performance and mechanism

Abstract: The heterogeneous Fenton-like catalysts biochar modified CuFeO2 (CuFeO2/BC) were fabricated by hydrothermal method without additional chemical reducing agent. The systematic characterization demonstrated that higher CuFeO2 particles dispersion and larger BET surface area of CuFeO2/BC catalyst contributed to higher catalytic activity towards the tetracycline (TC) degradation compared to pure-phase CuFeO2. The optimum conditions for TC removal were 598.63 mg L-1 of CuFeO2/BC-1.0, 57.63 mM of H2O2 and pH = 6.27 according to the result of a response surface methodology based on the central composite design. The CuFeO2/BC-1.0 exhibited an excellent reusability and good stability by recycling degradation. The OH was evidenced to the main active radical by scavenging experiments and electron spin resonance. The XPS revealed that the high catalytic efficiency was attributed to the synergistic effect of Fe3+/Fe2+ and Cu2+/Cu+ redox cycles, and the degradation intermediates of TC and toxicity analysis were evaluated.

Electronic metal-support interaction modulates single-atom platinum catalysis for hydrogen evolution reaction.

Abstract: Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts. Insights into the rational design of single-atom metal catalysts remains obscure in heterogeneous catalysis. Here, the authors establish the atomic-level structure–activity relationship for a wide-pH-range hydrogen evolution reaction through the electronic metal–support interaction modulation.

Chemical vapour deposition of Fe-N-C oxygen reduction catalysts with full utilization of dense Fe-N4 sites.

Abstract: Replacing scarce and expensive platinum (Pt) with metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has largely been impeded by the low oxygen reduction reaction activity of M–N–C due to low active site density and site utilization. Herein, we overcome these limits by implementing chemical vapour deposition to synthesize Fe–N–C by flowing iron chloride vapour over a Zn–N–C substrate at 750 °C, leading to high-temperature trans-metalation of Zn–N4 sites into Fe–N4 sites. Characterization by multiple techniques shows that all Fe–N4 sites formed via this approach are gas-phase and electrochemically accessible. As a result, the Fe–N–C catalyst has an active site density of 1.92 × 1020 sites per gram with 100% site utilization. This catalyst delivers an unprecedented oxygen reduction reaction activity of 33 mA cm−2 at 0.90 V (iR-corrected; i, current; R, resistance) in a H2–O2 proton exchange membrane fuel cell at 1.0 bar and 80 °C. Replacing platinum with metal–nitrogen–carbon catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has been impeded by low activity. These limitations have now been overcome by the trans-metalation of Zn–N4 sites into Fe–N4 sites.

Engineering single-atomic ruthenium catalytic sites on defective nickel-iron layered double hydroxide for overall water splitting.

Abstract: Rational design of single atom catalyst is critical for efficient sustainable energy conversion. However, the atomic-level control of active sites is essential for electrocatalytic materials in alkaline electrolyte. Moreover, well-defined surface structures lead to in-depth understanding of catalytic mechanisms. Herein, we report a single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets (Ru1/D-NiFe LDH). Under precise regulation of local coordination environments of catalytically active sites and the existence of the defects, Ru1/D-NiFe LDH delivers an ultralow overpotential of 18 mV at 10 mA cm−2 for hydrogen evolution reaction, surpassing the commercial Pt/C catalyst. Density functional theory calculations reveal that Ru1/D-NiFe LDH optimizes the adsorption energies of intermediates for hydrogen evolution reaction and promotes the O–O coupling at a Ru–O active site for oxygen evolution reaction. The Ru1/D-NiFe LDH as an ideal model reveals superior water splitting performance with potential for the development of promising water-alkali electrocatalysts. Rational design of single atom catalyst is critical for efficient sustainable energy conversion. Single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets achieve superior HER and OER performance in alkaline media.

Platinum single-atom catalyst coupled with transition metal/metal oxide heterostructure for accelerating alkaline hydrogen evolution reaction.

Abstract: Single-atom catalysts provide an effective approach to reduce the amount of precious metals meanwhile maintain their catalytic activity. However, the sluggish activity of the catalysts for alkaline water dissociation has hampered advances in highly efficient hydrogen production. Herein, we develop a single-atom platinum immobilized NiO/Ni heterostructure (PtSA-NiO/Ni) as an alkaline hydrogen evolution catalyst. It is found that Pt single atom coupled with NiO/Ni heterostructure enables the tunable binding abilities of hydroxyl ions (OH*) and hydrogen (H*), which efficiently tailors the water dissociation energy and promotes the H* conversion for accelerating alkaline hydrogen evolution reaction. A further enhancement is achieved by constructing PtSA-NiO/Ni nanosheets on Ag nanowires to form a hierarchical three-dimensional morphology. Consequently, the fabricated PtSA-NiO/Ni catalyst displays high alkaline hydrogen evolution performances with a quite high mass activity of 20.6 A mg−1 for Pt at the overpotential of 100 mV, significantly outperforming the reported catalysts. While H2 evolution from water may represent a renewable energy source, there is a strong need to improve catalytic efficiencies while maximizing materials utilization. Here, authors examine single-atom Pt on nickel-based heterostructures as highly active electrocatalysts for alkaline H2 evolution.

MIL-101-Derived Mesoporous Carbon Supporting Highly Exposed Fe Single-Atom Sites as Efficient Oxygen Reduction Reaction Catalysts.

Abstract: Fe single-atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal-organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF-derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2 -MIL-101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N-doped carbon supports (denoted herein as NC-MIL101-T) with a well-defined mesoporous structure at different pyrolysis temperatures. The NC-MIL101-T supports are then impregnated with a Fe(II)-phenanthroline complex, and heated again to yield Fe SAC-MIL101-T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC-MIL101-1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half-wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc-air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn -1 ) and solid-state zinc-air batteries (a peak power density of 50.6 mW cm-2 and a specific capacity of 724.0 mAh kgZn -1 ).

Electrochemical CO2-to-ethylene conversion on polyamine-incorporated Cu electrodes

Abstract: Electrochemical conversion of CO2 into value-added chemicals holds promise to enable the transition to carbon neutrality. Enhancing selectivity for a specific hydrocarbon product is challenging, however, due to numerous possible reaction pathways of CO2 electroreduction. Here we present a Cu–polyamine hybrid catalyst, developed through co-electroplating, that significantly increases the selectivity for ethylene production. The Faradaic efficiency for ethylene production is 87% ± 3% at −0.47 V versus reversible hydrogen electrode, with full-cell energetic efficiency reaching 50% ± 2%. Raman measurements indicate that the polyamine entrained on the Cu electrode results in higher surface pH, higher CO content and higher stabilization of intermediates compared with entrainment of additives containing little or no amine functionality. More broadly, this work shows that polymer incorporation can alter surface reactivity and lead to enhanced product selectivity at high current densities. Electrochemical conversion of CO2 into value-added chemicals holds promise to enable the transition to carbon neutrality, but enhancing the selectivity toward a specific hydrocarbon product remains a challenging task. Now, the authors present a Cu–polyamine hybrid catalyst that achieves Faradaic efficiency of 87% for ethylene and full-cell energy efficiency of 50%.

Propane dehydrogenation: catalyst development, new chemistry, and emerging technologies

Abstract: Propylene is an important building block for enormous petrochemicals including polypropylene, propylene oxide, acrylonitrile and so forth. Propane dehydrogenation (PDH) is an industrial technology for direct propylene production which has received extensive attention in recent years. With the development of dehydrogenation technologies, the efficient adsorption/activation of propane and subsequential desorption of propylene on the surfaces of heterogeneous catalysts remain scientifically challenging. This review describes recent advances in the fundamental understandings of the PDH process in terms of emerging technologies, catalyst development and new chemistry in regulating the catalyst structures and inhibiting the catalyst deactivation. The active sites, reaction pathways and deactivation mechanisms of PDH over metals and metal oxides as well as their dependent factors are also analysed and discussed, which is expected to enable efficient catalyst design for minimizing the reaction barriers and controlling the selectivity towards propylene. The challenges and perspectives of PDH over heterogeneous catalysts are also proposed for further development.

Single Atom Ruthenium-Doped CoP/CDs Nanosheets via Splicing of Carbon-Dots for Robust Hydrogen Production

Abstract: Ultrathin two-dimensional catalysts are attracting attention in the field of electrocatalytic hydrogen evolution. This work describe a composite material design in which CoP nanoparticles doped with Ru single-atom sites supported on carbon dots (CDs) single-layer nanosheets formed by splicing CDs (Ru CoP/CDs). Small CD fragments bore abundant functional groups, analogous to pieces of a jigsaw puzzle, and could provide a high density of binding sites to immobilize Ru CoP. The single-particle-thick nanosheets formed by splicing CDs acted as supports, which improved the conductivity of the electrocatalyst and the stability of the catalyst during operation. The Ru CoP/CDs formed from doping atomic Ru dispersed on CoP showed very high efficiency for the hydrogen evolution reaction (HER) over a wide pH range. The catalyst prepared under optimized conditions displayed outstanding stability and activity: the overpotential for the HER at a current density of 10 mA cm was as low as 51 and 49 mV under alkaline and acidic conditions, respectively. Density functional theory calculations showed that the substituted Ru single atoms lowered the proton-coupled electron transfer energy barrier and promoted H−H bond formation, thereby enhancing catalytic performance for the HER. The findings open a new avenue for developing carbon-based hybridization materials with integrated electrocatalytic performance for water splitting. 1 1 1 −2

Operando Cooperated Catalytic Mechanism of Atomically Dispersed Cu-N4 and Zn-N4 for Promoting Oxygen Reduction Reaction.

Abstract: Dual-metal single-atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual-metal single-atom catalyst consisted of Cu-N4 and Zn-N4 on the N-doped carbon support (Cu/Zn-NC). It exhibits high-efficiency ORR activity with an Eonset of 0.98 V and an E1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state-of-the-art Pt/C and great mass of Pt-free single atom catalysts. Operando XANES demonstrates that the Cu-N4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn-N4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d-orbital electron distribution of Cu could benefit to the stretch and cleavage of O-O on Cu active center, speeding up the process of rate determining step of OOH*.

Cobalt single atom site catalysts with ultrahigh metal loading for enhanced aerobic oxidation of ethylbenzene

Abstract: The oxidation of hydrocarbons to produce high value-added compounds (ketones or alcohols) using oxygen in air as the only oxidant is an efficient synthetic strategy from both environmental and economic views. Herein, we successfully synthesized cobalt single atom site catalysts (Co SACs) with high metal loading of 23.58 wt.% supported on carbon nitride (CN), which showed excellent catalytic properties for oxidation of ethylbenzene in air. Moreover, Co SACs show a much higher turn-over frequency (19.6 h−1) than other reported non-noble catalysts under the same condition. Comparatively, the as-obtained nanosized or homogenous Co catalysts are inert to this reaction. Co SACs also exhibit high selectivity (97%) and stability (unchanged after five runs) in this reaction. DFT calculations reveal that Co SACs show a low energy barrier in the first elementary step and a high resistance to water, which result in the robust catalytic performance for this reaction.

A stable low-temperature H2-production catalyst by crowding Pt on α-MoC.

Abstract: The water–gas shift (WGS) reaction is an industrially important source of pure hydrogen (H2) at the expense of carbon monoxide and water1,2. This reaction is of interest for fuel-cell applications, but requires WGS catalysts that are durable and highly active at low temperatures3. Here we demonstrate that the structure (Pt1–Ptn)/α-MoC, where isolated platinum atoms (Pt1) and subnanometre platinum clusters (Ptn) are stabilized on α-molybdenum carbide (α-MoC), catalyses the WGS reaction even at 313 kelvin, with a hydrogen-production pathway involving direct carbon monoxide dissociation identified. We find that it is critical to crowd the α-MoC surface with Pt1 and Ptn species, which prevents oxidation of the support that would cause catalyst deactivation, as seen with gold/α-MoC (ref. 4), and gives our system high stability and a high metal-normalized turnover number of 4,300,000 moles of hydrogen per mole of platinum. We anticipate that the strategy demonstrated here will be pivotal for the design of highly active and stable catalysts for effective activation of important molecules such as water and carbon monoxide for energy production. A stable, low-temperature water–gas shift catalyst is achieved by crowding platinum atoms and clusters on α-molybdenum carbide; the crowding protects the support from oxidation that would cause catalyst deactivation.

Enhancing carbon dioxide gas-diffusion electrolysis by creating a hydrophobic catalyst microenvironment.

Abstract: Electroreduction of carbon dioxide (CO2) over copper-based catalysts provides an attractive approach for sustainable fuel production. While efforts are focused on developing catalytic materials, it is also critical to understand and control the microenvironment around catalytic sites, which can mediate the transport of reaction species and influence reaction pathways. Here, we show that a hydrophobic microenvironment can significantly enhance CO2 gas-diffusion electrolysis. For proof-of-concept, we use commercial copper nanoparticles and disperse hydrophobic polytetrafluoroethylene (PTFE) nanoparticles inside the catalyst layer. Consequently, the PTFE-added electrode achieves a greatly improved activity and Faradaic efficiency for CO2 reduction, with a partial current density >250 mA cm-2 and a single-pass conversion of 14% at moderate potentials, which are around twice that of a regular electrode without added PTFE. The improvement is attributed to a balanced gas/liquid microenvironment that reduces the diffusion layer thickness, accelerates CO2 mass transport, and increases CO2 local concentration for the electrolysis.

The promoting effect of H2O on rod-like MnCeOx derived from MOFs for toluene oxidation: A combined experimental and theoretical investigation

Abstract: Herein, a series of rod-like MnCeOx are synthesized by pyrolyzing Mn/Ce-BTC for toluene oxidation. The 3Mn2Ce catalyst exhibits superior catalytic performance and stability under high humidity (10 % H2O). XRD, Raman, H2-TPR, O2-TPD, XPS and EXAFS results confirm that the formation of solid solution between Ce and Mn species and better reducibility play a key role in toluene oxidation. H2O-TPD, toluene-TPD, toluene-TPSR, in situ DRIFTS in different conditions and TD-GC–MS confirm that the introduction of water can promote toluene mineralization. H2O-TPD indicates that oxygen vacancies adsorbed H2O to provide HOH active sites and promote the conversion of Oads to Olatt. The degradation pathway of toluene was toluene→benzaldehyde→benzoate→CO2 and H2O. Additionally, the water promotion is also confirmed by DFT calculations. The promotion of water vapor is that the water vapor is conducive to the adsorption of toluene, benzaldehyde and oxygen, and promotes the activation of oxygen.

Sulfur vacancy-rich MoS2 as a catalyst for the hydrogenation of CO2 to methanol

Abstract: The low-temperature hydrogenation of CO2 to methanol is of great significance for the recycling of this greenhouse gas to valuable products, however, it remains a great challenge due to the trade-off between catalytic activity and selectivity. Here, we report that CO2 can dissociate at sulfur vacancies in MoS2 nanosheets to yield surface-bound CO and O at room temperature, thus enabling a highly efficient low-temperature hydrogenation of CO2 to methanol. Multiple in situ spectroscopic and microscopic characterizations combined with theoretical calculations demonstrated that in-plane sulfur vacancies drive the selective hydrogenation of CO2 to methanol by inhibiting deep hydrogenolysis to methane, whereas edge vacancies facilitate excessive hydrogenation to methane. At 180 °C, the catalyst achieved a 94.3% methanol selectivity at a CO2 conversion of 12.5% over the in-plane sulfur vacancy-rich MoS2 nanosheets, which notably surpasses those of previously reported catalysts. This catalyst exhibited high stability for over 3,000 hours without any deactivation, rendering it a promising candidate for industrial application. The catalytic hydrogenation of CO2 to methanol is a crucial reaction for the recycling of this greenhouse gas, although the selection and related performance of commercial catalysts is still limited. Now, the authors introduce sulfur vacancy-rich MoS2 nanosheets as a superior catalyst for this process, rivalling the commercial benchmark system.

Advanced Electrocatalysis for Energy and Environmental Sustainability via Water and Nitrogen Reactions

Abstract: Clean and efficient energy storage and conversion via sustainable water and nitrogen reactions have attracted substantial attention to address the energy and environmental issues due to the overwhelming use of fossil fuels. These electrochemical reactions are crucial for desirable clean energy technologies, including advanced water electrolyzers, hydrogen fuel cells, and ammonia electrosynthesis and utilization. Their sluggish reaction kinetics lead to inefficient energy conversion. Innovative electrocatalysis, i.e., catalysis at the interface between the electrode and electrolyte to facilitate charge transfer and mass transport, plays a vital role in boosting energy conversion efficiency and providing sufficient performance and durability for these energy technologies. Herein, a comprehensive review on recent progress, achievements, and remaining challenges for these electrocatalysis processes related to water (i.e., oxygen evolution reaction, OER, and oxygen reduction reaction, ORR) and nitrogen (i.e., nitrogen reduction reaction, NRR, for ammonia synthesis and ammonia oxidation reaction, AOR, for energy utilization) is provided. Catalysts, electrolytes, and interfaces between the two within electrodes for these electrocatalysis processes are discussed. The primary emphasis is device performance of OER-related proton exchange membrane (PEM) electrolyzers, ORR-related PEM fuel cells, NRR-driven ammonia electrosynthesis from water and nitrogen, and AOR-related direct ammonia fuel cells.

Sulfur-anchoring synthesis of platinum intermetallic nanoparticle catalysts for fuel cells.

Abstract: Atomically ordered intermetallic nanoparticles are promising for catalytic applications but are difficult to produce because the high-temperature annealing required for atom ordering inevitably acc...

Pt/Fe2O3 with Pt–Fe pair sites as a catalyst for oxygen reduction with ultralow Pt loading

Abstract: Platinum is the archetypal electrocatalyst for oxygen reduction—a key reaction in fuel cells and zinc–air batteries. Although dispersing platinum as single atoms on a support is a promising way to minimize the amount required, catalytic activity and selectivity are often low due to unfavourable O2 adsorption. Here we load platinum onto α-Fe2O3 to construct a highly active and stable catalyst with dispersed Pt–Fe pair sites. We propose that the Pt–Fe pair sites have partially occupied orbitals driven by strong electronic coupling, and can cooperatively adsorb O2 and dissociate the O=O bond, whereas OH* can desorb from the platinum site. In alkaline conditions, the catalyst exhibits onset and half-wave potentials of 1.15 V and 1.05 V (versus the reversible hydrogen electrode), respectively, mass activity of 14.9 A mg−1Pt (at 0.95 V) and negligible activity decay after 50,000 cycles. It also shows better performance than 20% Pt/C in a zinc–air battery and H2–O2 fuel cell in terms of specific energy density and platinum utilization efficiency. Atomically dispersed platinum electrocatalysts for oxygen reduction promise minimized platinum usage, but catalytic activity and selectivity are often low due to unfavourable O2 adsorption. To circumvent this issue, Gao and colleagues load platinum onto α-Fe2O3, making a highly active and stable catalyst with dispersed Pt–Fe pair sites.

Nickel ferrocyanide as a high-performance urea oxidation electrocatalyst

Abstract: Urea is often present in waste water but can be used in powering fuel cells and as an alternative oxidation substrate to water in an electrolyser. However, an insufficient mechanistic understanding and the lack of efficient catalysts for the urea oxidation reaction have hampered the development of such applications. Here we demonstrate that a nickel ferrocyanide (Ni2Fe(CN)6) catalyst supported on Ni foam can drive the urea oxidation reaction with a higher activity and better stability than those of conventional Ni-based catalysts. Our experimental and computational data suggest a urea oxidation reaction pathway different from most other Ni-based catalysts that comprise NiOOH derivatives as the catalytically active compound. Ni2Fe(CN)6 appears to be able to directly facilitate a two-stage reaction pathway that involves an intermediate ammonia production (on the Ni site) and its decomposition to N2 (on the Fe site). Owing to the different rate-determining steps with more favourable thermal/kinetic energetics, Ni2Fe(CN)6 achieves a 100 mA cm−2 anodic current density at a potential of 1.35 V (equal to an overpotential of 0.98 V). Urea oxidation could be a lower-energy alternative to water oxidation in hydrogen-producing electrolysers, but improved catalysts are required to facilitate the reaction. Geng et al. report nickel ferrocyanide as a promising catalyst and suggest that it operates via a different pathway to that of previous materials.

Stable and Highly Efficient Hydrogen Evolution from Seawater Enabled by an Unsaturated Nickel Surface Nitride

Abstract: Electrocatalytic production of hydrogen from seawater provides a route to low-cost and clean energy conversion. However, the hydrogen evolution reaction (HER) using seawater is greatly hindered by the lack of active and stable catalysts. Herein, an unsaturated nickel surface nitride (Ni-SN@C) catalyst that is active and stable for the HER in alkaline seawater is prepared. It achieves a low overpotential of 23 mV at a current density of 10 mA cm-2 in alkaline seawater electrolyte, which is superior to Pt/C. Compared to conventional transition metal nitrides or metal/metal nitride heterostructures, the Ni-SN@C has no detectable bulk nickel nitride phase. Instead, unsaturated NiN bonding on the surface is present. In situ Raman measurements show that the Ni-SN@C performs like Pt with the ability to generate hydronium ions in a high-pH electrolyte. The catalyst operation is then demonstrated in a two-electrode electrolyzer system, coupling with hydrazine oxidation at the anode. Using this system, a cell voltage of only 0.7 V is required to achieve a current density of 1 A cm-2 .

Exploiting Ru-Induced Lattice Strain in CoRu Nanoalloys for Robust Bifunctional Hydrogen Production.

Abstract: Designing bifunctional catalysts capable of driving the electrochemical hydrogen evolution reaction (HER) and also H2 evolution via the hydrolysis of hydrogen storage materials such as ammonia borane (AB) is of considerable practical importance for future hydrogen economies. Herein, we systematically examined the effect of tensile lattice strain in CoRu nanoalloys supported on carbon quantum dots (CoRu/CQDs) on hydrogen generation by HER and AB hydrolysis. By varying the Ru content, the lattice parameters and Ru-induced lattice strain in the CoRu nanoalloys could be tuned. The CoRu0.5 /CQDs catalyst with an ultra-low Ru content (1.33 wt.%) exhibited excellent catalytic activity for HER (η=18 mV at 10 mA cm-2 in 1 M KOH) and extraordinary activity for the hydrolysis of AB with a turnover frequency of 3255.4 mol ( H 2 ) mol-1 (Ru) min-1 or 814.7 mol ( H 2 ) mol-1 (cat) min-1 at 298 K, respectively, representing one of the best activities yet reported for AB hydrolysis over a ruthenium alloy catalyst. Moreover, the CoRu0.5 /CQDs catalyst displayed excellent stability during each reaction, including seven alternating cycles of HER and AB hydrolysis. Theoretical calculations revealed that the remarkable catalytic performance of CoRu0.5 /CQDs resulted from the optimal alloy electronic structure realized by incorporating small amounts of Ru, which enabled fast interfacial electron transfer to intermediates, thus benefitting H2 evolution kinetics. Results support the development of new and improved catalysts HER and AB hydrolysis.

Novel lignin-based single atom catalysts as peroxymonosulfate activator for pollutants degradation: Role of single cobalt and electron transfer pathway

Abstract: In this work, a facile one-pot pyrolytic strategy was employed to fabricate a nitrogen coordinated Co single-atom catalyst (SA Co-N/C catalyst) by using lignin as carbon sources. The HAADF-STEM images and X-ray absorption spectra (XAS) analysis showed the isolated Co atoms less than 2 A throughout the entire SA Co-N/C architecture. Results showed that the single-atom Co sites served as the main active sites for naproxen (NPX) degradation via peroxymonosulfate (PMS) activation. This was confirmed by the high positive correlation (R2 = 0.9675) between the rate constants and Co amounts in all SA Co-N/C catalysts. In particular, the as-prepared SA Co-N/C catalyst with a very small Co loading (2.45 wt.%) exhibited exceptional high turnover frequency (TOF) value for NPX (4.82 min−1), which is promising for the potential application prospect. Electron transfer was induced by the single-atom Co sites, which was the dominated mechanism for the NPX degradation.

Interface dynamics of Pd–CeO2 single-atom catalysts during CO oxidation

Abstract: In recent years, noble metals atomically dispersed on solid oxide supports have become a frontier of heterogeneous catalysis. In pursuit of an ultimate atom efficiency, the stability of single-atom catalysts is pivotal. Here we compare two Pd/CeO2 single-atom catalysts that are active in low-temperature CO oxidation and display drastically different structural dynamics under the reaction conditions. These catalysts were obtained by conventional impregnation on hydrothermally synthesized CeO2 and one-step flame spray pyrolysis. The oxidized Pd atoms in the impregnated catalyst were prone to reduction and sintering during CO oxidation, whereas they remained intact on the surface of the Pd-doped CeO2 derived by flame spray pyrolysis. A detailed in situ characterization linked the stability of the Pd single atoms to the reducibility of the Pd–CeO2 interface and the extent of reverse oxygen spillover. To understand the chemical phenomena that underlie the metal–support interactions is crucial to the rational design of stable single-atom catalysts. Single-atom catalysts have become a frontier of heterogeneous catalysis, but to achieve a high stability under turnover is often a challenge. Now, a Pd/CeO2 single-atom catalyst prepared using flame spray pyrolysis is able to stabilize the isolated Pd species during CO oxidation due to a high mobility of surface lattice oxygen.

Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

Abstract: Developing efficient and stable earth-abundant electrocatalysts for acidic oxygen evolution reaction is the bottleneck for water splitting using proton exchange membrane electrolyzers. Here, we show that nanocrystalline CeO2 in a Co3O4/CeO2 nanocomposite can modify the redox properties of Co3O4 and enhances its intrinsic oxygen evolution reaction activity, and combine electrochemical and structural characterizations including kinetic isotope effect, pH- and temperature-dependence, in situ Raman and ex situ X-ray absorption spectroscopy analyses to understand the origin. The local bonding environment of Co3O4 can be modified after the introduction of nanocrystalline CeO2, which allows the CoIII species to be easily oxidized into catalytically active CoIV species, bypassing the potential-determining surface reconstruction process. Co3O4/CeO2 displays a comparable stability to Co3O4 thus breaks the activity/stability tradeoff. This work not only establishes an efficient earth-abundant catalysts for acidic oxygen evolution reaction, but also provides strategies for designing more active catalysts for other reactions.

RhSe 2 : A Superior 3D Electrocatalyst with Multiple Active Facets for Hydrogen Evolution Reaction in Both Acid and Alkaline Solutions

Abstract: Layered 2D materials are a vital class of electrocatalys for the hydrogen evolution reaction (HER), due to their large area, excellent activity, and facile fabrication. Theoretical caculations domenstrate, however, that only the edges of the 2D nanosheets act as active sites, while the much larger basal plane exhibits passive activity. Here, from a distinguishing perspective, RhSe2 is reported as a "3D" electrocatalyst for HER with top-class activity, synthesized by a facile solid-state method. Superior to 2D materials, multiple crystal facets of RhSe2 exhibit near-zero free energy change of hydrogen adsorption (ΔGH ), which guarantees high performance in most common morphologies. Density functional theory calculations reveal that the low-coordinated Rh atoms act as the active sites in acid, which enables the modified Kubas-mediated pathway, while the Se atoms act as the active sites in an alkaline medium. The overpotentials of HER activity of RhSe2 are measured to be 49.9 and 81.6 mV at 10 mA cm-2 in acid and alkaline solutions, respectively. This work paves the way to new transition metal chalcogenide catalysts.

High-valent bimetal Ni3S2/Co3S4 induced by Cu doping for bifunctional electrocatalytic water splitting

Abstract: Rational design of low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for renewable energy conversion. Herein, for the first time, a facile strategy is developed to synthesize M (M = Fe, Cu, Zn, Mo) doped bimetallic sulfide heterostructure Ni3S2/Co3S4 electrocatalysts. The as-prepared bifunctional Cu-Ni3S2/Co3S4 electrode exhibits excellent electrocatalytic activity for HER and OER in 1 M KOH electrolyte, and it requires only an overpotential of 79 mV (150 mV) to deliver 10 mA cm−2 (20 mA cm-2) current density for HER process. Moreover, it shows a considerable low cell voltage of 1.49 V at the current density of 10 mA cm-2 in a two-electrode configuration which is far surpassing most of the reported bifunctional metal sulfides. Meanwhile, besides increasing the specific surface area of the electrocatalyst by optimizing the microstructure, the introduction of Cu cation could also stimulate the formation of high-valent Ni/Co sites, which can be verified by XPS technique. Density function theory calculations demonstrate that the Cu-doping boosts the formation of high valent Co sites and enhances the charge transfer performance of Ni and Co species, thus promotes intrinsic catalytic activity through modulating the d-band center of Co and reducing the adsorption energy of H and O-containing intermediates (H*, OH*, OOH*) on the surface of the catalyst. This work suggests the importance of exploitation of transition metal ion-doping for promoting the electrocatalytic activity of bimetallic sulfides.