A Study of Gas Diffusion Electrodes for the Coupled Reaction of Water Electrolysis and Electrocatalytic Benzene Hydrogenation

Gas diffusion electrodes are applied to the coupled reaction of water electrolysis and electrocatalytic benzene hydrogenation. The effects of the preparation conditions of electrodes, electrolyte acidity, the concentration of benzene and water vapor, and the flow rate of N2 are investigated by evaluating the efficiency of the current. Furthermore, the optimal operational conditions have been ascertained. The results of our experiment show that gas diffusion electrodes have good performance when the content of PTFE is 10% (wt) and that of Nafion is 0.75mg/cm2. The optimal operational conditions are as follows: The temperature of electrolysis is 70℃, acidity 0.5mol/L, the concentration of benzene 26%, the concentration of vapor 10%, the flow rate of N2 80mL/min-240mL/min. The efficiency of the current can reach 35% under optimal operational conditions. Then, a conclusion can be drawn that gas diffusion electrodes can improve the rate of the coupled reaction effectively.

Electrochemical disinfection using the gas diffusion electrode system

A study on the electrochemical disinfection with H202 generated at the gas diffusion electrode （GDE） from active carbon/poly- tetrafluoroethylene was performed in a non-membrane cell. The effects of Pt load and the pore-forming agent content in GDE, and operating conditions were investigated. The experimental results showed that nearly all bacterial cultures inoculated in the secondary effluent from wastewater treatment plant could be inactivated within 30 min at a current density of 10 mA/cm^2. The disinfection improved with increasing Pt load. Addition of the pore-forming agent NH4HCO3 improved the disinfection, while a drop in the pH value resulted in a rapid rise of germicidal efficacy and the disinfection time was shortened with increasing oxygen flow rate. Adsorption was proved to be ineffective in destroying bacteria, while germicidal efficacy increased with current density. The acceleration rate was different, it initially increased with current density. Then decreased, and finally reached a maximum at a current density of 6.7 mA/cm^2. The disinfection also improved with decreasing total bacterial count. The germicidal efficacy in the cathode compartment was approximately the same as in the anode compartment, indicating that the contribution of direct oxidation and the indirect treatment of bacterial cultures by hydroxyl radical was similar to the oxidative indirect effect of the generated H2O2.

Electrocatalytic CO_(2) reduction to C_(2)H_(4): From lab to fab

The global concerns of energy crisis and climate change,primarily caused by carbon dioxide(CO_(2)),are of utmost importance.Recently,the electrocatalytic CO_(2) reduction reaction(CO_(2)RR) to high value-added multi-carbon(C_(2+)) products driven by renewable electricity has emerged as a highly promising solution to alleviate energy shortages and achieve carbon neutrality.Among these C_(2+) products,ethylene(C_(2)H_(4))holds particular importance in the petrochemical industry.Accordingly,this review aims to establish a connection between the fundamentals of electrocatalytic CO_(2) reduction reaction to ethylene(CO_(2)RRto-C_(2)H_(4)) in laboratory-scale research(lab) and its potential applications in industrial-level fabrication(fab).The review begins by summarizing the fundamental aspects,including the design strategies of high-performance Cu-based electrocatalysts and advanced electrolyzer devices.Subsequently,innovative and value-added techniques are presented to address the inherent challenges encountered during the implementations of CO_(2)RR-to-C_(2)H_(4) in industrial scenarios.Additionally,case studies of the technoeconomic analysis of the CO_(2)RR-to-C_(2)H_(4) process are discussed,taking into factors such as costeffectiveness,scalability,and market potential.The review concludes by outlining the perspectives and challenges associated with scaling up the CO_(2)RR-to-C_(2)H_(4) process.The insights presented in this review are expected to make a valuable contribution in advancing the CO_(2)RR-to-C_(2)H_(4) process from lab to fab.

Gas diffusion in catalyst layer of flow cell for CO_(2) electroreduction toward C_(2+) products

The use of gas diffusion electrode(GDE)based flow cell can realize industrial-scale CO_(2) reduction reactions(CO_(2)RRs).Controlling local CO_(2) and CO intermediate diffusion plays a key role in CO_(2)RR toward multi-carbon(C_(2+))products.In this work,local CO_(2) and CO intermediate diffusion through the catalyst layer(CL)was investigated for improving CO_(2)RR toward C_(2+)products.The gas permeability tests and finite element simulation results indicated CL can balance the CO_(2) gas diffusion and residence time of the CO intermediate,leading to a sufficient CO concentration with a suitable CO_(2)/H_(2)O supply for high C_(2+)products.As a result,an excellent selectivity of C_(2+)products~79%at a high current density of 400 mA·cm^(-2) could be obtained on the optimal 500 nm Cu CL(Cu500).This work provides a new insight into the optimization of CO_(2)/H_(2)O supply and local CO concentration by controlling CL for C_(2+)products in CO_(2)RR flow cell.

气体扩散电极电合成过氧化氢技术研究进展

过氧化氢(H_(2)O_(2))是一种高效的氧化剂,被广泛应用于化学合成、消毒杀菌和废水处理.通过二电子氧还原反应(2e^(-)ORR)原位电合成H_(2)O_(2)的方法具有高性能和环保性,可作为传统蒽醌工艺的替代策略.气体扩散电极(GDEs)可作为阴极,通过电催化生产H_(2)O_(2),具有更低的成本、更低的能耗和更高的氧气利用效率等优点.探讨GDEs作为阴极时通过2e^(-)ORR产H_(2)O_(2)的机制;讨论GDEs的基本构型、原理及优化方法;分析GDEs催化剂的种类及优势;展望了GDEs作为阴极原位制备H_(2)O_(2)时存在的挑战,为推动2e^(-)ORR原位电合成H_(2)O_(2)迈向市场化提供借鉴.

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N_(2) reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N_(2) molecules and the limited supply of N_(2) to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N_(2) molecules.The eNRR system is further modified using a gas diffusion electrode(GDE) coated with polytetrafluoroethylene(PTFE) to form an effective three-phase boundary of liquid water-gas N_(2)-solid catalyst to facilitate easy access of N_(2) to the catalytic sites.As a result,the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH_(3) production rate of 7.69 μg h^(-1) cm^(-2) at-0.2 V_(RHE),which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell.This work represents a successful demonstration of dual modification strategies;catalyst modification and N_(2) supplying system engineering,and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.

Microbial electrosynthesis of acetate from CO_(2)in three-chamber cells with gas diffusion biocathode under moderate saline conditions

The industrial adoption of microbial electrosynthesis(MES)is hindered by high overpotentials deriving from low electrolyte conductivity and inefficient cell designs.In this study,a mixed microbial consortium originating from an anaerobic digester operated under saline conditions(∼13 g L^(−1)NaCl)was adapted for acetate production from bicarbonate in galvanostatic(0.25 mA cm^(−2))H-type cells at 5,10,15,or 20 g L^(−1)NaCl concentration.The acetogenic communities were successfully enriched only at 5 and 10 g L^(−1)NaCl,revealing an inhibitory threshold of about 6 g L^(−1)Na^(+).The enriched planktonic communities were then used as inoculum for 3D printed,three-chamber cells equipped with a gas diffusion biocathode.The cells were fed with CO_(2)gas and operated galvanostatically(0.25 or 1.00 mA cm^(−2)).The highest production rate of 55.4 g m^(−2) d^(−1)(0.89 g L^(−1)d^(−1)),with 82.4%Coulombic efficiency,was obtained at 5 g L^(−1)NaCl concentration and 1 mA cm^(−2)applied current,achieving an average acetate production of 44.7 kg MWh−1.Scanning electron microscopy and 16S rRNA sequencing analysis confirmed the formation of a cathodic biofilm dominated by Acetobacterium sp.Finally,three 3D printed cells were hydraulically connected in series to simulate an MES stack,achieving three-fold production rates than with the single cell at 0.25 mA cm^(−2).This confirms that three-chamber MES cells are an efficient and scalable technology for CO_(2)bio-electro recycling to acetate and that moderate saline conditions(5 g L^(−1)NaCl)can help reduce their power demand while preserving the activity of acetogens.

CO_(2)electrolysis:Advances and challenges in electrocatalyst engineering and reactor design

Electrochemical reduction of CO_(2)(CO_(2)RR)coupled with renewable electrical energy is an attractive way of upgrading CO_(2)to value-added chemicals and closing the carbon cycle.However,CO_(2)RR electrocatalysts still suffer from high overpotential,and the complex reaction pathways of CO_(2)RR often lead to mixed products.Early research focuses on tuning the binding of reaction intermediates on electrocatalysts,and recent efforts have revealed that the design of electrolysis reactors is equally important for efficient and selective CO_(2)RR.In this review,we present an overview of recent advances and challenges toward achieving high activity and high selectivity in CO_(2)RR at ambient conditions,with a particular focus on the progress of CO_(2)RR electrocatalyst engineering and reactor design.Our discussion begins with three types of electrocatalysts for CO_(2)RR(noble metalbased,none-noble metal-based,and metal-free electrocatalysts),and then we examine systems-level strategies toward engineering specific components of the electrolyzer,including gas diffusion electrodes,electrolytes,and polymer electrolyte membranes.We close with future perspectives on catalyst development,in-situ/operando characterization,and electrolyzer performance evaluation in CO_(2)RR studies.

Advances and challenges of electrolyzers for large-scale CO_(2) electroreduction

CO_(2) electroreduction(CO_(2) ER)to high value-added chemicals is considered as a promising technology to achieve sustainable carbon neutralization.By virtue of the progressive research in recent years aiming at design and understanding of catalytic materials and electrolyte systems,the CO_(2) ER performance(such as current density,selectivity,stability,CO_(2) conversion,etc.)has been continually increased.Unfortunately,there has been relatively little attention paid to the large-scale CO 2 electrolyzers,which stand just as one obstacle,alongside series-parallel integration,challenging the practical application of this infant technology.In this review,the latest progress on the structures of low-temperature CO_(2) electrolyzers and scale-up studies was systematically overviewed.The influence of the CO_(2) electrolyzer configurations,such as the flow channel design,gas diffusion electrode(GDE)and ion exchange membrane(IEM),on the CO_(2) ER performance was further discussed.The review could provide inspiration for the design of large-scale CO_(2) electrolyzers so as to accelerate the industrial application of CO_(2) ER technology.

3D打印气体扩散电极产H2O2及其对焦化废水的处理研究

利用3D打印技术设计出一种高效产H_2O_2的3D打印气体扩散电极(3D-GDE)并将其应用于电芬顿体系对实际焦化废水降解研究.结果表明3D-GDE阴极H_2O_2产量高达16.1mgH_2O_2/cm2,而相同条件下传统气体扩散电极仅为7.16mgH_2O_2/cm2.通过考察不同因素对阴极产H_2O_2影响可知:酸性条件更有利于产H_2O_2;电流从200mA提高到250mA,其H_2O_2产量从250mg/L提高到450mg/L,但是继续提高电流时(250～300m A),H_2O_2并没有明显增加.将3D-GDE电极应用于电芬顿对实际焦化废水处理,在最适宜条件下,可以实现对焦化废水有效矿化(4h电解后高达80%),其降解过程中三维荧光指纹分析也直接证明了该体系的高效性.Microtox毒性实验表明,3D-GDE电芬顿体系可以有效的降低焦化废水体系的毒性,其最低能耗为0.9kW·h/g TOC.

A comprehensive assessment on the durability of gas diffusion electrode materials in PEM fuel cell stack

Polymer electrolyte membrane (PEM) fuel cell is the most promising among the various types of fuel cells. Though it has found its applications in numerous fields, the cost and durability are key barriers impeding the commercialization of PEM fuel cell stack. The crucial and expensive component involved in it is the gas diffusion electrode (GDE) and its degradation, which limits the performance and life of the fuel cell stack. A critical analysis and comprehensive understanding of the struc-tural and functional properties of various materials involved in the GDE can help us to address the related durability and cost issues. This paper reviews the key GDE components, and in specific, the root causes influencing the durability. It also envisages the role of novel materials and provides a critical recommendation to improve the GDE durability.

新型电化学体系对4-氯苯酚的降解

实验构建了4种电化学反应体系,考察了各体系降解4-氯苯酚的效果.结果表明,以Sb-SnO2/Ti和Fe板为双阳极、多壁碳纳米管气体电极为阴极构建的新型电催化-电Fenton-电絮凝复合反应体系中,4-氯苯酚的去除率最高.通过正交实验确定了该体系各主要参数对4-氯苯酚去除率的影响程度由大到小依次为初始浓度>曝气量>pH值>电流密度.在阳极电流密度为20mA/cm2、曝气量为1.3L/min、pH值为3的条件下,初始浓度100mg/L的4-氯苯酚在电解10min时的去除率为96%.

Preparation of a Pb loaded gas diffusion electrode and its application to C02 electroreduction

A Pb loaded gas diffusion electrode was fabricated and used for the electroreduction of CO2 to formic acid. The Pb/C catalyst was prepared by isometric impregnation. The crystal structure and morphology of the Pb/C catalyst were characterized by X-ray diffraction （XRD） and transmission electron microscope （TEM）. The preparation conditions of the gas diffusion electrode were optimized by adjusting the amounts of polytetrafluoroethylene （PTFE） in the gas diffusion layer and acetylene black in the catalytic layer. The electrochemical performance of the as-prepared gas diffusion electrode was studied by chronoamperometry and cyclic voltammetry. The optimized gas diffusion electrode showed good catalytic performance for the electroreduction of CO2. The current efficiency of formic acid after 1 h of operation reached a maximum of 22% at -2.0 V versus saturated calomel electrode （SCE）.

Innovative strategies toward challenges in PV-powered electrochemical CO_(2)reduction

The solar energy-driven electrochemical CO_(2)reduction to value-added fuels or chemicals is considered as an attractive path to store renewable energy in the form of chemical energy to close the carbon cycle.However,CO_(2)reduction suffers from a number of challenges including slow reaction rates,low selectivity,and low energy conversion efficiency.Recently,innovative strategies have been developed to mitigate this challenges.Especially the development of flow cell reactors with a gas diffusion electrode,ionic liquid electrolytes,and new electrocatalysts have dramatically improved the reaction rates and selectivity to desired products.In this perspective,we highlight the key recent developments and challenges in PVpowered electrochemical CO_(2)reduction and propose effective strategies to improve the reaction kinetics,to minimize the electrical energy losses,and to tune the selectivity of the catalysts for desired products,and then suggest future direction of research and development.

Performance Investigation of Membrane Electrode Assemblies for High Temperature Proton Exchange Membrane Fuel Cell

Different types of ABPBI (poly(2,5-benzimidazole)) membranes and polymer binders were evaluated to investigate the performance of MEAs for high temperature proton exchange membrane fuel cell (HT-PEMFC). The properties of the prepared MEAs were evaluated and analyzed by polarization curve, electrochemistry impedance spectroscopy (EIS), cyclic voltammetry (CV) and durability test. The results showed that MEA with modified ABPBI membrane (AM) has satisfactory performance and durability for fuel cell application. Compare to conventional PBI or Nafion binders, polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as binders in the catalyst layer (CL) of gas diffusion electrode (GDE) for HT-PEMFC.

Janus electrode with simultaneous management on gas and liquid transport for boosting oxygen reduction reaction

Oxygen reduction efficiency holds the key for renewable energy technologies including fuel cells and metal-air batteries,which involves coupling diffusion-reaction-conduction processes at the interface of catalyst/electrolyte,and thus rational electrode design facilitating mass transportation stands as a key issue for fast oxygen reduction reaction(ORR).Herein,we report a Janus electrode with asymmetric wettability prepared by partly modifying aerophobic nitrogen doped carbon nanotube arrays with polytetrafluoroethylene(PTFE)as a high performance catalytic electrode for ORR.The Janus electrode with opposite wettability on adjacent sides maintains stable gas reservoir in the aerophilic side while shortening O2 pathway to catalysts in the aerophobic side,resulting in superior ORR performance(22.5 mA/cm^2@0.5 V)than merely aerophilic or aerophilic electrodes.The Janus electrode endows catalytic performance even comparable to commercial,Pt/C in the alkali ne electrolyte,exploiting a previously unrecognized opport unity that guides electrode design for the gas-consumption electrocatalysis.

Evaluation of the technoeconomic feasibility of electrochemical hydrogen peroxide production for decentralized water treatment

This study evaluated the feasibility of electrochemical hydrogen peroxide(H2O2)production with gas diffusion electrode(GDE)for decentralized water treatment.Carbon black-polytetrafluoroethylene GDEs were prepared and tested in a continuous flow electrochemical cell for H2O2 production from oxygen reduction.Results showed that because of the effective oxygen transfer in GDEs,the electrode maintained high apparent current efficiencies(ACEs,>80%)for H_(2)O_(2) production over a wide current density range of 5–400 mA/cm^(2),and H_(2)O_(2) production rates as high as~202 mg/h/cm^(2) could be obtained.Long-term stability test showed that the GDE maintained high ACEs(>85%)and low energy consumption(<10 kWh/kg H2O2)for H_(2)O_(2) production for 42 d(~1000 h).However,the ACEs then decreased to~70%in the following 4 days because water flooding of GDE pores considerably impeded oxygen transport at the late stage of the trial.Based on an electrode lifetime of 46 days,the overall cost for H2O2 production was estimated to be~0.88$/kg H_(2)O_(2),including an electricity cost of 0.61$/kg and an electrode capital cost of 0.27$/kg.With a 9 cm^(2) GDE and 40 mA/cm^(2) current density,~2–4 mg/L of H2O2 could be produced on site for the electro-peroxone treatment of a 1.2 m^(3)/d groundwater flow,which considerably enhanced ibuprofen abatement compared with ozonation alone(~43%–59%vs.7%).These findings suggest that electrochemical H_(2)O_(2) production with GDEs holds great promise for the development of compact treatment technologies for decentralized water treatment at a household and community level.