Textured Asymmetric Membrane Electrode Assemblies of Piezoelectric Phosphorene and Ti_(3)C_(2)T_(x)MXene Heterostructures for Enhanced Electrochemical Stability and Kinetics in LIBs

Black phosphorus with a superior theoretical capacity(2596 mAh g^(-1))and high conductivity is regarded as one of the powerful candidates for lithium-ion battery(LIB)anode materials,whereas the severe volume expansion and sluggish kinetics still impede its applications in LIBs.By contrast,the exfoliated two-dimensional phosphorene owns negligible volume variation,and its intrinsic piezoelectricity is considered to be beneficial to the Li-ion transfer kinetics,while its positive influence has not been discussed yet.Herein,a phosphorene/MXene heterostructure-textured nanopiezocomposite is proposed with even phosphorene distribution and enhanced piezo-electrochemical coupling as an applicable free-standing asymmetric membrane electrode beyond the skin effect for enhanced Li-ion storage.The experimental and simulation analysis reveals that the embedded phosphorene nanosheets not only provide abundant active sites for Li-ions,but also endow the nanocomposite with favorable piezoelectricity,thus promoting the Li-ion transfer kinetics by generating the piezoelectric field serving as an extra accelerator.By waltzing with the MXene framework,the optimized electrode exhibits enhanced kinetics and stability,achieving stable cycling performances for 1,000 cycles at 2 A g^(-1),and delivering a high reversible capacity of 524 m Ah g^(-1)at-20℃,indicating the positive influence of the structural merits of self-assembled nanopiezocomposites on promoting stability and kinetics.

Recent advances in Pt catalysts and membrane electrode assemblies fabrication for proton exchange membrane fuel cells

Proton exchange membrane fuel cells(PEMFCs)have been identified as a highly promising means of achieving sustainable energy conversion.A crucial factor in enhancing the performance of PEMFCs for further potential energy applications is the advancement in the field of catalyst engineering that has led to remarkable performance enhancement in facilitating the oxygen reduction reaction(ORR).Subsequently,it is important to acknowledge that the techniques used in preparation of membrane electrode assemblies(MEAs),the vital constituents of PEMFCs,also possess direct and critical influence on exhibiting the full catalytic activity of meticulously crafted catalysts.Here,a succinct summary of the most recent advancements in Pt catalysts for ORR was offered and their underly catalytic mechanism were discussed.Then,both laboratory-scale and industrial-scale MEA fabrication techniques of Pt catalysts were summarized.Furthermore,a detailed analysis of the connections between materials,process,and performance in MEA fabrication was presented in order to facilitate the development of optimal catalyst layers.

Surface promotion of copper nanoparticles with alumina clusters derived from layered double hydroxide accelerates CO_(2)reduction to ethylene in membrane electrode assemblies

Electrochemical CO_(2)reduction has the vast potential to neutralize CO_(2)emission and valorizes this greenhouse gas into chemicals and fuels under mild conditions.Its commercial realization hinges on catalyst innovation as well as device engineering for enabling reactions at industrially relevant conditions.Copper has been widely examined for the selective production of multicarbon chemicals particularly ethylene,while there is still a substantial gap between the expected and the attainable.In this work,we report that the surface promotion of copper with alumina clusters is a viable strategy to enhance its electrocatalytic performance.AlOx-promoted Cu catalyst is derived from Cu-Al layered double hydroxide nanosheets after alkali etching and cathodic conversion.It can catalyze CO_(2)to ethylene and multicarbon products with great selectivity and stability far superior to pristine copper in both an H-cell and a zero-gap membrane electrode assembly(MEA)electrolyzer.The surface promotion effect is understood via computational simulations showing that alumina clusters can stabilize key reaction intermediates(*COOH and*OCCOH)along the reaction pathway.

Designing Membrane Electrode Assembly for Electrochemical CO_(2)Reduction:a Review

Currently, the electrochemical CO_(2) reduction reaction (CO_(2) RR) can realize the resource conversion of CO_(2) , which is a promising approach to carbon resource use. Important advancements have been made in exploring the CO_(2) RR performance and mechanism because of the rational design of electrolyzer systems, such as H-cells, flow cells, and catalysts. Considering the future development direction of this technology and large-scale application needs, membrane electrode assembly (MEA) systems can improve energy use efficiency and achieve large-scale CO_(2) conversion, which is considered the most promising technology for industrial applications. This review will concentrate on the research progress and present situation of the MEA component structure. This paper begins with the composition and construction of a gas diff usion electrode. Then, the application of ion-exchange membranes in MEA is introduced. Furthermore, the eff ects of pH and the anion and cation of the anolyte on MEA performance are explored. Additionally, we present the anode reaction type in MEA. Finally, the challenges in this field are summarized, and upcoming trends are projected. This review should offer researchers a clearer picture of MEA systems and provide important, timely, and valuable insights into rational electrolyzer design to facilitate further development of CO_(2) electrochemical reduction.

Progress and perspective of single-atom catalysts for membrane electrode assembly of fuel cells

A fuel cell is an energy conversion device that can continuously input fuel and oxidant into the device through an electrochemical reaction to release electrical energy.Although noble metals show good activity in fuel cell-related electrochemical reactions,their ever-increasing price considerably hinders their industrial application.Improvement of atom utilization efficiency is considered one of the most effective strategies to improve the mass activity of catalysts,and this allows for the use of fewer catalysts,saving greatly on the cost.Thus,single-atom catalysts(SACs)with an atom utilization efficiency of 100%have been widely developed,which show remarkable performance in fuel cells.In this review,we will describe recent progress on the development of SACs for membrane electrode assembly of fuel cell applications.First,we will introduce several effective routes for the synthesis of SACs.The reaction mechanism of the involved reactions will also be introduced as it is highly determinant of the final activity.Then,we will systematically summarize the application of Pt group metal(PGM)and nonprecious group metal(non-PGM)catalysts in membrane electrode assembly of fuel cells.This review will offer numerous experiences for developing potential industrialized fuel cell catalysts in the future.

Enhancement of current density using effective membranes electrode assemblies for water electrolyser system

The goal of this study was to develop and design a composite proton exchange membrane（PEM） and membrane electrode assembly（MEA） that are suitable for the PEM based water electrolysis system. In particular,it focuses on the development of sulphonated polyether ether ketone（SPEEK） based membranes and caesium salt of silico-tungstic acid（Cs Si WA） matrix compared with one of the transition metal oxides such as titanium dioxide（TiO2）, silicon dioxide（SiO2） and zirconium dioxide（ZrO2）. The resultant membranes have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, ion exchange capacity（IEC）, water uptake and atomic force microscopy. Comparative studies on the performance of MEAs were also conducted utilizing impregnation-reduction and conventional brush coating methods. The PEM electrolysis performance of SPEEK-Cs Si WA-ZrO2 composite membrane was more superior than that of other membranes involved in this study. Electrochemical characterization shows that a maximum current density of 1.4 A/cm^2 was achieved at 60 °C, explained by an increased concentration of protonic sites available at the interface.

Probing the Efficiency of PPMG-Based Composite Electrolytes for Applications of Proton Exchange Membrane Fuel Cell

PPMG-based composite electrolytes were fabricated via the solution method using the polyvinyl alcohol and polyvinylpyrrolidone blend reinforced with various contents of sulfonated inorganic filler.Sulfuric acid was employed as the sulfonating agent to functionalize the external surface of the inorganic filler,i.e.,graphene oxide.The proton conductivities of the newly prepared proton exchange membranes(PEMs)were increased by increasing the temperature and content of sulfonated graphene oxide(SGO),i.e.,ranging from 0.025 S/cm to 0.060 S/cm.The induction of the optimum level of SGO is determined to be an excellent route to enhance ionic conductivity.The single-cell performance test was conducted by sandwiching the newly prepared PEMs between an anode(0.2 mg/cm^(2) Pt/Ru)and a cathode(0.2 mg/cm^(2) Pt)to prepare membrane electrode assemblies,followed by hot pressing under a pressure of approximately 100 kg/cm^(2) at 60℃for 5–10 min.The highest power densities achieved with PPMG PEMs were 14.9 and 35.60 mW/cm^(2) at 25℃and 70℃,respectively,at ambient pressure with 100%relative humidity.Results showed that the newly prepared PEMs exhibit good electrochemical performance.The results indicated that the prepared composite membrane with 6 wt%filler can be used as an alternative membrane for applications of high-performance proton exchange membrane fuel cell.

PtNi-W/C with Atomically Dispersed Tungsten Sites Toward Boosted ORR in Proton Exchange Membrane Fuel Cell Devices

The performance of proton exchange membrane fuel cells is heavily dependent on the microstructure of electrode catalyst especially at low catalyst loadings.This work shows a hybrid electrocatalyst consisting of PtNi-W alloy nanocrystals loaded on carbon surface with atomically dispersed W sites by a two-step straightforward method.Single-atomic W can be found on the carbon surface,which can form protonic acid sites and establish an extended proton transport network at the catalyst surface.When implemented in membrane electrode assembly as cathode at ultra-low loading of 0.05 mgPt cm^(−2),the peak power density of the cell is enhanced by 64.4%compared to that with the commercial Pt/C catalyst.The theoretical calculation suggests that the single-atomic W possesses a favorable energetics toward the formation of*OOH whereby the intermediates can be efficiently converted and further reduced to water,revealing a interfacial cascade catalysis facilitated by the single-atomic W.This work highlights a novel functional hybrid electrocatalyst design from the atomic level that enables to solve the bottle-neck issues at device level.

Technical factors affecting the performance of anion exchange membrane water electrolyzer

Anion exchange membrane(AEM)electrolysis is a promising membrane-based green hydrogen production technology.However,AEM electrolysis still remains in its infancy,and the performance of AEM electrolyzers is far behind that of well-developed alkaline and proton exchange membrane electrolyzers.Therefore,breaking through the technical barriers of AEM electrolyzers is critical.On the basis of the analysis of the electrochemical performance tested in a single cell,electrochemical impedance spectroscopy,and the number of active sites,we evaluated the main technical factors that affect AEM electrolyzers.These factors included catalyst layer manufacturing(e.g.,catalyst,carbon black,and anionic ionomer)loadings,membrane electrode assembly,and testing conditions(e.g.,the KOH concentration in the electrolyte,electrolyte feeding mode,and operating temperature).The underlying mechanisms of the effects of these factors on AEM electrolyzer performance were also revealed.The irreversible voltage loss in the AEM electrolyzer was concluded to be mainly associated with the kinetics of the electrode reaction and the transport of electrons,ions,and gas-phase products involved in electrolysis.Based on the study results,the performance and stability of AEM electrolyzers were significantly improved.

A cascade of in situ conversion of bicarbonate to CO_(2) and CO_(2) electroreduction in a flow cell with a Ni-N-S catalyst

Combination of CO_(2) capture using inorganic alkali with subsequently electrochemical conversion of the resultant HCO_(3)^(-)to high-value chemicals is a promising route of low cost and high efficiency.The electrochemical reduction of HCO_(3)^(-)is challenging due to the inaccessible of negatively charged molecular groups to the electrode surface.Herein,we adopt a comprehensive strategy to tackle this challenge,i.e.,cascade of in situ chemical conversion of HCO_(3)^(-)to CO_(2) and CO_(2) electrochemical reduction in a flow cell.With a tailored Ni-N-S single atom catalyst(SACs),where sulfur(S)atoms located in the second shell of Ni center,the CO_(2)electroreduction(CO_(2)ER)to CO is boosted.The experimental results and density functional theory(DFT)calculations reveal that the introduction of S increases the p electron density of N atoms near Ni atom,thereby stabilizing^(*)H over N and boosting the first proton coupled electron transfer process of CO_(2)ER,i.e.,^(*)+e^(-)+^(*)H+^(*)CO_(2)→^(*)COOH.As a result,the obtained catalyst exhibits a high faradaic efficiency(FE_(CO)~98%)and a low overpotential of 425 mV for CO production as well as a superior turnover frequency(TOF)of 47397 h^(-1),outcompeting most of the reported Ni SACs.More importantly,an extremely high FECOof 90%is achieved at 50 mA cm^(-2)in the designed membrane electrode assembly(MEA)cascade electrolyzer fed with liquid bicarbonate.This work not only highlights the significant role of the second coordination on the first coordination shell of the central metal for CO_(2)ER,but also provides an alternative and feasible strategy to realize the electrochemical conversion of HCO_(3)^(-)to high-value chemicals.

High-performance proton exchange membrane fuel cell with ultra-low loading Pt on vertically aligned carbon nanotubes as integrated catalyst layer

Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure of catalyst layers with efficient mass transportation channels plays a vital role.Herein,PEMFCs with order-structured cathodic electrodes were fabricated by depositing Pt nanoparticles by Ebeam onto vertically aligned carbon nanotubes(VACNTs)growth on Al foil via plasma-enhanced chemical vapor deposition.Results demonstrate that the proportion of hydrophilic Pt-deposited region along VACNTs and residual hydrophobic region of VANCTs without Pt strongly influences the cell performance,in particular at high current densities.When Pt nanoparticles deposit on the top depth of around 600 nm on VACNTs with a length of 4.6μm,the cell shows the highest performance,compared with others with various lengths of VACNTs.It delivers a maximum power output of 1.61 W cm^(-2)(H_(2)/O_(2),150 k Pa)and 0.79 W cm^(-2)(H_(2)/Air,150 k Pa)at Pt loading of 50μg cm^(-2),exceeding most of previously reported PEMFCs with Pt loading of<100μg cm^(-2).Even though the Pt loading is down to 30μg cm^(-2)(1.36 W cm^(-2)),the performance is also better than 100μg cm^(-2)(1.24 W cm^(-2))of commercial Pt/C,and presents better stability.This excellent performance is critical attributed to the ordered hydrophobic region providing sufficient mass passages to facilitate the fast water drainage at high current densities.This work gives a new understanding for oxygen reduction reaction occurred in VACNTs-based ordered electrodes,demonstrating the most possibility to achieve a substantial reduction in Pt loading<100μg cm^(-2) without sacrificing in performance.

Novel phosphonated polymer without anhydride formation for proton exchange membrane fuel cells

Proton exchange membrane fuel cells(PEMFCs)are regarded as one of the most promising clean energy technology because of their high energy density,silent emission-free operation,and wide applications[1].Recently,anion exchange membrane fuel cells(AEMFCs)has emerged as an alternative to PEMFCs.

Segmented tomographic evaluation of structural degradation of carbon support in proton exchange membrane fuel cells

The variation of the three-dimensional(3D)structure of the membrane electrode of a fuel cell during proton exchange cycling involves the corrosion/compaction of the carbon support.The increasing degradation of the carbon structure continuously reduces the electrocatalytic performance of proton exchange membrane fuel cells(PEM-FCs).This phenomenon can be explained by performing 3D tomographic analysis at the nanoscale.However,conventional tomographic approaches which present limited experimental feasibility,cannot perform such evaluation and have not provided sufficient structural information with statistical significance thus far.Therefore,a reliable methodology is required for the 3D geometrical evaluation of the carbon structure.Here,we propose a segmented tomographic approach which employs pore network analysis that enables the visualization of the geometrical parameters corresponding to the porous carbon structure at a high resolution.This approach can be utilized to evaluate the 3D structural degradation of the porous carbon structure after cycling in terms of local surface area,pore size distribution,and their 3D networking.These geometrical parameters of the carbon body were demonstrated to be substantially reduced owing to the cycling-induced degradation.This information enables a deeper understanding of the degradation phenomenon of carbon supports and can contribute to the development of stable PEM-FC electrodes.

Passive electrochemical hydrogen recombiner for hydrogen safety systems:prospects

This paper presents the concept of a passive electrochemical hydrogen recombiner(PEHR).The reaction energy of the recombination of hydrogen and oxygen is used as a source of electrical energy according to the operating principle for hydrogen fuel cells to establish forced circulation of the hydrogen mixture as an alternative to natural circulation(as is not utilized in conventional passive autocatalytic hydrogen recombiners currently used in nuclear power plants(NPPs)).The proposed concept of applying the physical operation principles of a PEHR based on a fuel cell simultaneously increases both productivity in terms of recombined hydrogen and the concentration threshold of flameless operation(the‘ignition’limit).Thus,it is possible to reliably ensure the hydrogen explosion safety of NPPs under all conditions,including beyond-design accidents.An experimental setup was assembled to test a laboratory sample of a membrane electrode assembly(MEA)at various hydrogen concentrations near the catalytic surfaces of the electrodes,and the corresponding current–voltage characteristics were recorded.The simplest MEA based on the Advent P1100W PBI membrane demonstrated stable performance(delivery of electrical power)over a wide range of hydrogen concentrations.

氢燃料电池关键零部件MEA的选型验证

氢燃料电池电堆降本举措是我国氢燃料电池行业发展的重中之重,关键零部件的国产化则是诸多降本举措中的重要环节。本文通过研究国产MEA选型和验证的案例,从燃料电池膜电极的发电性能、低温性能以及衰减和耐久等几个方面,对燃料电池工程化过程中MEA关键技术指标验证和确定提供了指导。

Enhancing proton exchange membrane water electrolysis by building electron/proton pathways

Proton exchange membrane water electrolysis(PEMWE)plays a critical role in practical hydrogen production.Except for the electrode activities,the widespread deployment of PEMWE is severely obstructed by the poor electron-proton permeability across the catalyst layer(CL)and the inefficient transport structure.In this work,the PEDOT:F(Poly(3,4-ethylenedioxythiophene):perfluorosulfonic acid)ionomers with mixed proton-electron conductor(MPEC)were fabricated,which allows for a homogeneous anodic CL structure and the construction of a highly efficient triple-phase interface.The PEDOT:F exhibits strong perfluorosulfonic acid(PFSA)side chain extensibility,enabling the formation of large hydrophilic ion clusters that form proton-electron transport channels within the CL networks,thus contributing to the surface reactant water adsorption.The PEMWE device employing membrane electrode assembly(MEA)prepared by PEDOT:F-2 demonstrates a competitive voltage of 1.713 V under a water-splitting current of 2 A cm^(-2)(1.746 V at 2A cm^(-2) for MEA prepared by Nafion D520),along with exceptional long-term stability.Meanwhile,the MEA prepared by PEDOT:F-2 also exhibits lower ohmic resistance,which is reduced by 23.4%and 17.6%at 0.1 A cm^(-2) and 1.5 A cm^(-2),respectively,as compared to the MEA prepared by D520.The augmentation can be ascribed to the superior proton and electron conductivity inherent in PEDOT:F,coupled with its remarkable structural stability.This characteristic enables expeditious mass transfer during electrolytic reactions,thereby enhancing the performance of PEMWE devices.

A Pair-Electrosynthesis for Formate at Ultra-Low Voltage Via Coupling of CO_(2) Reduction and Formaldehyde Oxidation

Formate can be synthesized electrochemically by CO_(2) reduction reaction(CO_(2)RR)or formalde-hyde oxidation reaction(FOR).The CO_(2)RR approach suffers from kinetic-sluggish oxygen evolution reac-tion at the anode.To this end,an electrochemical sys-tem combining cathodic CO_(2)RR with anodic FOR was developed,which enables the formate electrosynthesis at ultra-low voltage.Cathodic CO_(2)RR employing the BiOCl electrode in H-cell exhibited formate Faradaic efficiency(FE)higher than 90% within a wide potential range from−0.48 to−1.32 V_(RHE).In flow cell,the current density of 100 mA cm^(−2) was achieved at−0.67 V_(RHE).The anodic FOR using the Cu_(2)O electrode displayed a low onset potential of−0.13 V_(RHE) and nearly 100%formate and H_(2) selectivity from 0.05 to 0.35 V_(RHE).The CO_(2)RR and FOR were constructed in a flow cell through membrane electrode assembly for the electrosynthesis of formate,where the CO_(2)RR//FOR delivered an enhanced current density of 100 mA cm^(−2) at 0.86 V.This work provides a promising pair-electrosynthesis of value-added chemicals with high FE and low energy consumption.

Ni_(3)S_(2)@NiFePx electrode with dual-anion-modulated layer for efficient and stable oxygen evolution

The rational construction of high-performance and stable electrocatalyst for oxygen evolution reaction(OER)is a prerequisite for efficient water electrolysis.Herein,we develop a broccoli-like Ni_(3)S_(2)@NiFeP_(x)(Ni_(3)S_(2)@NFP)catalyst on nickel foam(NF)via a sequential two-step layer-by-layer assembly electrodeposition method.X-ray diffraction,in situ Raman and Fourier-transform infrared spectra have mutually validated the element segregation and phase refusion during OER condition.The reconstruction of double layer Ni_(3)S_(2)@NFP facilitates the formation of the active(oxy)hydroxides,which is modulated by the dual anionic layer with mixed sulfate and phosphate ions.As a result,the obtained Ni_(3)S_(2)@NFP electrode exhibits low overpotential(329 mV)and long-term durability(∼500 h)for OER at current density of 500mA/cm^(2).Moreover,the self-supported Ni_(3)S_(2)@NFP can act as an efficient and durable anode in alkaline anion exchange membrane water electrolysis device(AEMWE).This work provides a facile and scaled-up strategy to construct self-supported electrocatalyst and emphasizes the crucial role of anions in pre-catalyst reconstruction and enhancing OER performance.

Boosting the optimization of membrane electrode assembly in proton exchange membrane fuel cells guided by explainable artificial intelligence

The utilization of environmentally friendly hydrogen energy requires proton exchange membrane fuel cell de-vices that offer high power output while remaining affordable.However,the current optimization of their key component,i.e.,the membrane electrode assembly,is still based on intuition-guided,inefficient trial-and-error cycles due to its complexity.Hence,we introduce an innovative,explainable artificial intelligence(AI)tool trained as a reliable assistant for a variable analysis and optimum-value prediction.Among the 8 algorithms considered,the surrogate model built with an artificial neural network achieves high replaceability in the experimentally validated multiphysics simulation(R^(2)=0.99845)and a much lower computational cost.For interpretation,partial dependence plots and the Shapley value method are applied to black-box models to intelligently simulate the impact of each parameter on performance.These methods show that a tradeoff existed in the catalyst layer thickness.The AI-guided optimization suggestions regarding catalyst loading and the ion-omer content are fully supported by the experimental results,and the final product achieves 3.2 times the Pt utilization of commercial products with a time cost orders of magnitude smaller.

Proton antagonist membrane towards exclusive CO_(2)reduction

Membrane electrode assembly reactor offers great promise toward practical CO_(2)electrolysis.Unfortunately,traditional proton exchange membrane possesses strong acidic chemical environment,which facilitates undesired hydrogen evolution reaction.Here we report a proton antagonist strategy,through which the proton diffusion pathways have been severely impeded by Na+cation to produce an alkaline-rich environment.With this new membrane electrode assembly,we can significantly suppress the hydrogen evolution and achieve a Faradaic efficiency of 95.7%for CO with 51.5%energy efficiency.In addition,our proton antagonist membrane outperforms the commercial anion exchange membrane in both conductivity and oxidation resistance lifetime,which are crucial for large scale electrolysis of carbon neutral chemicals.