The influence of patterned microporous layer on the proton exchange membrane fuel cell performances

The ordered membrane electrode assembly(MEA)has gained much attention because of its potential in improving mass transfer.Here,a comprehensive study was conducted on the influence of the patterned microporous layer(MPL)on the proton exchange membrane fuel cell performances.When patterned MPL is employed,grooves are generated between the catalyst layer and the gas diffusion layer.It is found that the grooves do not increase the contact resistance,and it is beneficial for water retention.When the MEA works under low humidity scenarios,the MEA with patterned MPL illustrated higher performance,due to the reduced inner resistance caused by improved water retention,leading to increased ionic conductivity.However,when the humidity is higher than 80%or working under high current density,the generated water accumulated in the grooves and hindered the oxygen mass transport,leading to a reduced MEA performance.

Electrochemical converting ethanol to hydrogen and acetic acid for large scale green hydrogen production

Electrochemical coupling hydrogen evolution with biomass reforming reaction(named electrochemical hydrogen and chemical cogeneration(EHCC)),which realizes green hydrogen production and chemical upgrading simultaneously,is a promising method to build a carbon-neutral society.Herein,we analyze the EHCC process by considering the market assessment.The ethanol to acetic acid and hydrogen approach is the most feasible for large-scale hydrogen production.We develop AuCu nanocatalysts,which can selectively oxidize ethanol to acetic acid(>97%)with high long-term activity.The isotopic and in-situ infrared experiments reveal that the promoted water dissociation step by alloying contributes to the enhanced activity of the partial oxidation reaction path.A flow-cell electrolyzer equipped with the AuCu anodic catalyst achieves the steady production of hydrogen and acetic acid simultaneously in both high selectivity(>90%),demonstrating the potential scalable application for green hydrogen production with low energy consumption and high profitability.

Pt single atoms coupled with Ru nanoclusters enable robust hydrogen oxidation for high-performance anion exchange membrane fuel cells

The sluggish reaction kinetics of alkaline hydrogen oxidation reaction(HOR)is one of the key challenges for anion exchange membrane fuel cells(AEMFCs).To achieve robust alkaline HOR with minimized cost,we developed a single atom-cluster multiscale structure with isolated Pt single atoms anchored on Ru nanoclusters supported on nitrogen-doped carbon nanosheets(Pt1-Ru/NC).The well-defined structure not only provides multiple sites with varied affinity with the intermediates but also enables simultaneous modulation of different sites via interfacial interaction.In addition to weakening Ru–H bond strength,the isolated Pt sites are heavily involved in hydrogen adsorption and synergistically accelerate the Volmer step with the help of Ru sites.Furthermore,this catalyst configuration inhibits the excessive occupancy of oxygen-containing species on Ru sites and facilitates the HOR at elevated potentials.The Pt1-Ru/NC catalyst exhibits superior alkaline HOR performance with extremely high activity and excellent CO-tolerance.An AEMFC with a 0.1 mg·cmPGM^(−2)loading of Pt1-Ru/NC anode catalyst achieves a peak powder density of 1172 mW·cm^(−2),which is 2.17 and 1.55 times higher than that of Pt/C and PtRu/C,respectively.This work provides a new catalyst concept to address the sluggish kinetics of electrocatalytic reactions containing multiple intermediates and elemental steps.

A general and facile calcination method to synthesize single-site catalysts for highly efficient electrochemical CO_(2) reduction

The electrochemical CO_(2) reduction reaction(CO_(2)RR)has received widespread attention as a promising method for producing sustainable chemicals and mitigating the global warming.Here,we demonstrate a general and facile synthetic route for the metal-nitrogen-carbon(M-N-C)type catalyst by simply calcinating metal acetate and urea with commercial carbon black,which have potential application in CO_(2)RR.The synthesized Ni-NC-600 catalyst has the structure of single Ni atom coordinated with one N atom and three C atoms(Ni-N_(1)C_(3)),which is suggested by X-ray absorption spectroscopy.The Ni-NC-600 catalyst exhibits high CO_(2)RR catalytic performance and a high CO Faraday efficiency above 98%in a wide potential range from-0.7 to-1.3 V(vs.reversible hydrogen electrode(RHE)),superior to most of the reported Ni-N-C catalysts.This work has developed a facile strategy to synthesize high performance CO_(2)RR catalyst.

The difference of the ionomer–catalyst interfaces for poly(aryl piperidinium)hydroxide exchange membrane fuel cells and proton exchange membrane fuel cells

The microstructures of the ionomer–catalyst interfaces in the catalyst layers are important for the fuel cell performance because they determine the distribution of the active triple-phase boundaries.Here,we investigate the ionomer–catalyst interactions in hydroxide exchange membrane fuel cells(HEMFCs)using poly(aryl piperidinium)and compare them with proton exchange membrane fuel cells(PEMFCs).It is found that different catalyst layer microstructures are between the two types of fuel cell.The ionomer/carbon(I/C)ratio does not have a remarkable impact on the HEMFC performance,while it has a strong impact on the PEMFC performance,indicating the weaker interaction between the HEMFC ionomer and catalyst.Molecular dynamics simulations demonstrate that the HEMFC ionomer tends to distribute on the carbon support,unlike the PEMFC ionomer,which heavily covers the Pt nanoparticles.These results suggest that the poisoning effect of the ionomer on the catalyst is much weaker in HEMFCs,and the improved ionomer/catalyst interaction is beneficial for the HEMFC performances.

Improving the water electrolysis performance by manipulating the generated nano/micro-bubbles using surfactants

The impeded mass transfer rate by on-site-generated gas bubbles at both cathode and anode dramatically reduces the energy conversion efficiency of the proton exchange membrane water electrolyzer(PEMWE).Herein,we report a surfactant-assistant method to accelerate the nano/micro-bubble detachment and the mass transfer rate by reducing the surface tension,resulting in an increase in overall efficiency.Four kinds of surfactants are studied in this work.Only potassium perfluorobutyl sulfonate(PPFBS),which has the structural similarity to Nafion,shows a significant promotion of activity and stability for both hygrogen evolution reaction(HER)and oxygen evolution reaction(OER)in the acidic medium at the high current density region.The HER overpotential at 0.1 A·cm−2 decreased 22%,and the current density at−0.4 V increased 31%by adding PPFBS.The promotion of overall efficiency by PPFBS on a homemade PEMWE was also proven.The reduced surface tension and electrostatic repulsion were the probable origins of the accelerated bubble detachment.

Atomic Co/Ni dual sites with N/P-coordination as bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

Metal-nitrogen-carbon(M-N-C)single-atom catalysts exhibit desirable electrochemical catalytic properties.However,the replacement of N atoms by heteroatoms(B,P,S,etc.)has been regarded as a useful method for regulating the coordination environment.The structure engineered M-N-C sites via doping heteroatoms play an important role to the adsorption and activation of the oxygen intermediate.Herein,we develop an efficient strategy to construct dual atomic site catalysts via the formation of a Co_(1)-PN and Ni1-PN planar configuration.The developed Co_(1)-PNC/Ni1-PNC catalyst exhibits excellent bifunctional electrocatalytic performance in alkaline solution.Both experimental and theoretical results demonstrated that the N/P coordinated Co/Ni sites moderately reduced the binding interaction of oxygen intermediates.The Co_(1)-PNC/Ni1-PNC endows a rechargeable Zn-air battery with excellent power density and cycling stability as an air-cathode,which is superior to that of the benchmark Pt/C+IrO_(2).This work paves an avenue for design of dual single-atomic sites and regulation of the atomic configuration on carbon-based materials to achieve high-performance electrocatalysts.

Promoting the methanol oxidation catalytic activity by introducing surface nickel on platinum nanoparticles

High performance methanol oxidation reaction （MOR） catalysts are critical to the performance of attractive, direct methanol fuel cells. Here, we use surface controlled PtNi alloy nanoparticles as model catalysts to study the MOR mechanism and give further guidance to the design of new high performance MOR catalysts. The enhanced MOR activity of PtNi alloy was mainly attributed to the enhanced OH adsorption owing to surface Ni sites. This suggests that the MOR undergoes the Langmuir-Hinshelwood mechanism, whereby adsorbed CO is removed with the assistance of adsorbed OH. Within the PtNi catalyst, Pt provides methanol adsorption sites （in which methanol is converted to adsorbed CO） and Ni provides OH adsorption sites. The optimized Pt-Ni ratio for MOR was found to be 1：1. This suggests that bifunctional catalysts with both CO and OH adsorption sites can lead to highly active MOR catalysts.

PdAg bimetallic electrocatalyst for highly selective reduction of CO2 with low COOH^* formation energy and facile CO desorption

For electrocatalytic reduction of CO2 to CO,the stabilization of intermediate COOH^* and the desorption of CO^* are two key steps.Pd can easily stabilize COOH^*,whereas the strong CO^* binding to Pd surface results in severe poisoning,thus lowering catalytic activity and stability for CO2 reduction.On Ag surface,CO^* desorbs readily,while COOH^* requires a relatively high formation energy,leading to a high overpotential.In light of the above issues,we successfully designed the PdAg bimetallic catalyst to circumvent the drawbacks of sole Pd and Ag.The PdAg catalyst with Ag-terminated surface not only shows a much lower overpotential(-0.55 V with CO current density of 1 mA/cm^2)than Ag(−0.76 V),but also delivers a CO/H2 ratio 18 times as high as that for Pd at the potential of-0.75 V vs.RHE.The issue of CO poisoning is significantly alleviated on Ag-terminated PdAg surface,with the stability well retained after 4h electrolysis at-0.75 V vs.RHE.Density functional theory(DFT)calculations reveal that the Ag-terminated PdAg surface features a lowered formation energy for COOH^* and weakened adsorption for CO^*,which both contribute to the enhanced performance for CO2 reduction.

Direct synthesis of parallel doped N-MoP/N-CNT as highly active hydrogen evolution reaction catalyst

Doped phosphide is promising in earthabundant element based catalysts for hydrogen evolution reaction(HER). Here we employ ammonium hypophosphite(NH4H2PO2) to synthesize a novel parallel doped catalyst,nitrogen doped molybdenum phosphide nanoparticles(NPs)supported on nitrogen doped carbon nanotubes(N-MoP/N-CNTs). The NH4H2PO2 as a bifunctional agent severs as both phosphidation agent and nitrogen source, which makes the synthetic route simple and efficient. The as-obtained parallel doped N-MoP/N-CNTs show an overpotential of 103±5 mV at 10 mA cm-2, which is 140 mV lower than that of MoP NPs. The enhanced HER performance is attributed to the electronic effect by doped MoP and CNTs supports. This work provides a facile route to synthesize doped phosphides for the potential applications in hydrogen energy.

Amorphous M0S2 confined in nitrogen-doped porous carbon for improved electrocatalytic stability toward hydrogen evolution reaction

Developing non-precious metal catalysts with high activity and stability for electrochemical hydrogen evolution reaction(HER)is of great significance in both scie nee and tech no logy.In this work,N-doped CMK-3,which was prepared with a casting method using SBA-15 as thehard template and ammonia as the nitrogen source,has been utilized to hold MoS2 and restrict its growth to form MoS2@N-CMK-3 composite.As a result,M0S2 was found to have poorly crystallized and the limited space of porous N-CMK-3 made its size much small.Then there are moreactive sites in MoS2.Accordingly,MoS2@N-CMK-3 has exhibited good electrocatalytic performance toward HER in acids with a quite small Tafelslope of 32 mV·dec^-1.And more importantly,compared to MoS2@CMK-3,its stability has been greatly improved,which can be attributedto the interaction between M0S2 and nitrogen atoms avoiding aggregation and mass loss.This work provides an idea that doping a porouscarbon support with nitrogen is an effective way to enhance the stability of the catalyst.

Converting biomass into efficient oxygen reduction reaction catalysts for proton exchange membrane fuel cells

It is urgent to develop low-cost but efficient oxygen reduction reaction(ORR)catalysts for the emerging clean energy devices of fuel cells based on proton exchange membrane.Herein,we report a facile method to covert the biomass of black fungus into an efficient ORR catalyst.The black fungus undergoes hydrothermal and pyrolysis processes to transform into carbon-based materials.The as-obtained BF-N-950 catalyst shows prominent ORR catalytic activities in both acidic and alkaline electrolytes with a half-wave potential reaching 0.77 and 0.91 V,respectively.A membrane electrolyte assembly was fabricated with the as-obtained BF-N-950 as the cathode catalyst which shows a high peak power density of255 mW cm^-2.The study shows the potential of converting conventional biomass into low-cost ORR catalyst,which is promising for the fuel cell technology.

Photocatalytic hydrogenation of nitroarenes using Cu1.94S-Zn0.23Cd0.77S heteronanorods

Catalytic hydrogenation is an important process in the chemical industry. Traditional catalysts require the effective cleavage of hydrogen molecules on the metal-catalyst surface, which is difficult to achieve with non-noble metal catalysts. In this work, we report a new hydrogenation method based on water/ proton reduction, which is completely different from the catalytic cleavage of hydrogen molecules. Active hydrogen species and photo-generated electrons can be directly applied to the hydrogenation process with Cu1.94S-Zn0.23Cd0.775 semiconductor heterojunction nanorods. Nitrobenzene, with a variety of substituent groups, can be efficiently reduced to the corresponding aniline without the addition of hydrogen gas. This is a novel and direct pathway for hydrogenation using non-noble metal catalysts.

Silver based single atom catalyst with heteroatom coordination environment as high performance oxygen reduction reaction catalyst

Ag is a potential low-cost oxygen reduction reaction(ORR)catalyst in alkaline condition,which is important for the zinc-air batteries.Here,we report that an Ag based single atom catalyst with heteroatom coordination.Ag1-h-NPClSC,has been synthesized and shown much improved performance towards ORR by manipulating the coordination environment of the Ag center.It shows a high half wave potential(0.896 V)and a high turnover frequency(TOF)(5.9 s^(−1))at 0.85 V,which are higher than the previously reported Ag based catalysts and commercial Pt/C.A zinc-air battery with high peak power density of 270 mW·cm^(−2)is fabricated by using the Ag1-h-NPClSC as air electrode.The high performance is attributed to(1)the hollow structure providing good mass transfer;(2)the single atom metal center structure providing high utility of the Ag;(3)heteroatom coordination environment providing the adjusted binding to the ORR intermediates.Density functional theory(DFT)calculations show that the energy barrier for the formation of OOH*,which is considered as the rate determine step for ORR on Ag nanoparticles,is lowered on Ag1-h-NPClSC,thus improving the ORR activity.This work demonstrates that the well manipulated Ag based single atom catalysts are promising in electrocatalysis.

Defective Ni_(3)S_(2)nanowires as highly active electrocatalysts for ethanol oxidative upgrading

Electrochemical upgrading of biomass ethanol to value-added chemicals is promising for sustainable society.Here,we synthesize defective Ni_(3)S_(2) nanowires(NWs),which show high activity towards electrochemical oxidation of ethanol to acetate.The Ni_(3)S_(2) NWs are formed by the oriented attachment mechanism,and rich defects are introduced during the growth.A low onset potential of 1.31 V and high mass activity of 8,716 mA·mgNi^(-1) at 1.5 V are achieved using the synthesized Ni_(3)S_(2) NWs toward the ethanol electro-oxidation,which are better than the Ni(OH)2 NWs and the Ni_(3)S_(2) nanoparticles(NPs).And the selectivity for the acetate generation is ca.99%.The high activity of Ni_(3)S_(2) NWs is attributed to the easier oxidation of Ni(II)to the catalytically active Ni(III)species with the promotion from S component and rich defects.These results demonstrate that the defective NWs can be synthesized by the oriented attachment method and the defective Ni_(3)S_(2) NWs structure as the efficient nonnoble metal electrocatalysts for oxidative upgrading of ethanol.

Ultrathin NiFeS nanosheets as highly active electrocatalysts for oxygen evolution reaction

The development of efficient and cost-effective oxygen evolution reaction(OER)electrocatalysts is crucial for clean energy conversion and storage devices,such as water-splitting,CO_(2) reduction,and metalair batteries.Herein,we report an efficient 2-dimensional OER catalyst of ultrathin nickel-iron sulfide nanosheets(Ni Fe S-NS).Dodecanethiol is employed in the synthesis,which prohibits the growth along the Z-axis,thus a nanosheet is obtained.The Ni Fe S-NS shows high OER catalytic activity,which only requires a small overpotential of 273 mV to achieve the OER current density of 10 mA/cm^(2) in alkaline electrolyte,and almost no decay after 150 h of chronopotentiometry test.The high performance is attributed to the 2-dimensional structure,the synergistic effect from the Ni and Fe components which promotes the formation of the high valence Ni species,and the tuning effect from the in-situ generated sulfate doping.This work demonstrates the advantages of the 2-dimensional sulfides in electrocatalysis.