Deciphering engineering principle of three-phase interface for advanced gas-involved electrochemical reactions

As an alternative to conventional energy conversion and storage reactions,gas-involved electrochemical reactions,including the carbon dioxide reduction reaction(CO_(2)RR),nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER),have become an emerging research direction and have gained increasing attention due to their advantages of environmental friendliness and sustainability.Various studies have been designed to accelerate sluggish kinetics but with limited results.Most of them promote the reaction by modulating the intrinsic properties of the catalyst,ignoring the synergistic effect of the reaction as a whole.Due to the introduction of gas,traditional liquid-solid two-phase reactions are no longer applicable to future research.Since gas-involved electrochemical reactions mostly occur at the junctions of gaseous reactants,liquid electrolytes and solid catalysts,the focus of future research on reaction kinetics should gradually shift to three-phase reaction interfaces.In this review,we briefly introduce the formation and constraints of the three-phase interface and propose three criteria to judge its merit,namely,the active site,mass diffusion and electron mass transfer.Subsequently,a series of modulation methods and relevant works are discussed in detail from the three improvement directions of‘exposing more active sites,promoting mass diffusion and accelerating electron transfer’.Definitively,we provide farsighted insights into the understanding and research of three-phase interfaces in the future and point out the possible development direction of future regulatory methods,hoping that this review can broaden the future applications of the three-phase interface,including but not limited to gas-involved electrochemical reactions.

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently infl uence the catalytic perfor-mance.The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains,but related studies are lacking.Herein,a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofi bers with diff erent diameters,which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolu-tion reaction activities.Furthermore,the microstructure of electrocatalysts could infl uence the gas-liquid-solid interfacial mass transfer,resulting in diff erent electrochemical performances.

Advanced In Situ Characterization Techniques for Direct Observation of Gas-Involved Electrochemical Reactions

Gas-involved electrochemical reactions provide feasible solutions to the worldwide energy crisis and environmental pollution.It has been recognized that various elements of the reaction system,including catalysts,intermediates,and products,will undergo real-time variations during the reaction process,which are of significant meaning to the in-depth understanding of reaction mechanisms,material structure,and active sites.As judicious tools for real-time monitoring of the changes in these complex elements,in situ techniques have been exposed to the spotlight in recent years.This review aims to highlight significant progress of various advanced in situ characterization techniques,such as in situ X-ray based technologies,in situ spectrum technologies,and in situ scanning probe technologies,that enhance our understanding of heterogeneous electrocatalytic carbon dioxide reduction reaction,nitrogen reduction reaction,and hydrogen evolution reaction.We provide a summary of recent advances in the development and applications of these in situ characterization techniques,from the working principle and detection modes to detailed applications in different reactions,along with key questions that need to be addressed.Finally,in view of the unique application and limitation of different in situ characterization techniques,we conclude by putting forward some insights and perspectives on the development direction and emerging combinations in the future.

In situ observation of the electrochemical behavior of Li–CO_(2)/O_(2)batteries in an environmental transmission electron microscope

Li–CO_(2)/O_(2)batteries,a promising energy storage technology,not only provide ultrahigh discharge capacity but also capture CO_(2)and turn it into renewable energy.Their electrochemical reaction pathways'ambiguity,however,creates a hurdle for their practical application.This study used copper selenide(CuSe)nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO_(2)/O_(2)(mix CO_(2)as well as O_(2)at a volume ratio of 1:1)and Li–O_(2)batteries as well as Li–CO_(2)batteries.Primary discharge reactions take place successively in the Li–CO_(2)/O_(2)–CuSe nanobattery:(I)4Li^(+)+O_(2)+4e^(−)→2Li_(2)O;(II)Li_(2)O+CO_(2)→Li_(2)CO_(3).The charge reaction proceeded via(III)2Li_(2)CO_(3)→4Li^(+)+2CO_(2)+O_(2)+4e^(−).However,Li–O_(2)and Li–CO_(2)nanobatteries showed poor cycling stability,suggesting the difficulty in the direct decomposition of the discharge product.The fluctuations of the Li–CO_(2)/O_(2)battery's electrochemistry were also shown to depend heavily on O_(2).The CuSe‐based Li–CO_(2)/O_(2)battery showed exceptional electrochemical performance.The Li^–CO_(2)/O_(2)battery offered a discharge capacity apex of 15,492 mAh g^(−1) and stable cycling 60 times at 100 mA g^(−1).Our research offers crucial insight into the electrochemical behavior of Li–CO_(2)/O_(2),Li–O_(2),and Li–CO_(2)nanobatteries,which may help the creation of high‐performance Li–CO_(2)/O_(2)batteries for energy storage applications.

MOF‐derived 1D/3D N‐doped porous carbon for spatially confined electrochemical CO_(2) reduction to adjustable syngas

Electrochemical reduction of CO_(2) to syngas(CO and H_(2))offers an efficient way to mitigate carbon emissions and store intermittent renewable energy in chemicals.Herein,the hierarchical one‐dimensional/three‐dimensional nitrogen‐doped porous carbon(1D/3D NPC)is prepared by carbonizing the composite of Zn‐MOF‐74 crystals in situ grown on a commercial melamine sponge(MS),for electrochemical CO_(2) reduction reaction(CO_(2)RR).The 1D/3D NPC exhibits a high CO/H_(2) ratio(5.06)and CO yield(31 mmol g^(−1)h^(−1))at−0.55 V,which are 13.7 times and 21.4 times those of 1D porous carbon(derived from Zn‐MOF‐74)and N‐doped carbon(carbonized by MS),respectively.This is attributed to the unique spatial environment of 1D/3D NPC,which increases the adsorption capacity of CO_(2) and promotes electron transfer from the 3D N‐doped carbon framework to 1D carbon,improving the reaction kinetics of CO_(2)RR.Experimental results and charge density difference plots indicate that the active site of CO_(2)RR is the positively charged carbon atom adjacent to graphitic N on 1D carbon and the active site of HER is the pyridinic N on 1D carbon.The presence of pyridinic N and pyrrolic N reduces the number of electron transfer,decreasing the reaction kinetics and the activity of CO_(2)RR.The CO/H_(2) ratio is related to the distribution of N species and the specific surface area,which are determined by the degree of spatial confinement effect.The CO/H_(2) ratios can be regulated by adjusting the carbonization temperature to adjust the degree of spatial confinement effect.Given the low cost of feedstock and easy strategy,1D/3D NPC catalysts have great potential for industrial application.

Chalcogen heteroatoms doped nickel-nitrogen-carbon single-atom catalysts with asymmetric coordination for efficient electrochemical CO_(2) reduction

The electronic configuration of central metal atoms in single-atom catalysts(SACs)is pivotal in electrochemical CO_(2) reduction reaction(eCO_(2)RR).Herein,chalcogen heteroatoms(e.g.,S,Se,and Te)were incorporated into the symmetric nickel-nitrogen-carbon(Ni-N_(4)-C)configuration to obtain Ni-X-N_(3)-C(X:S,Se,and Te)SACs with asymmetric coordination presented for central Ni atoms.Among these obtained Ni-X-N_(3)-C(X:S,Se,and Te)SACs,Ni-Se-N_(3)-C exhibited superior eCO_(2)RR activity,with CO selectivity reaching~98% at-0.70 V versus reversible hydrogen electrode(RHE).The Zn-CO_(2) battery integrated with Ni-Se-N_(3)-C as cathode and Zn foil as anode achieved a peak power density of 1.82 mW cm^(-2) and maintained remarkable rechargeable stability over 20 h.In-situ spectral investigations and theoretical calculations demonstrated that the chalcogen heteroatoms doped into the Ni-N_(4)-C configuration would break coordination symmetry and trigger charge redistribution,and then regulate the intermediate behaviors and thermodynamic reaction pathways for eCO_(2)RR.Especially,for Ni-Se-N_(3)-C,the introduced Se atoms could significantly raise the d-band center of central Ni atoms and thus remarkably lower the energy barrier for the rate-determining step of ^(*)COOH formation,contributing to the promising eCO_(2)RR performance for high selectivity CO production by competing with hydrogen evolution reaction.

Bi-Atom Electrocatalyst for Electrochemical Nitrogen Reduction Reactions

The electrochemical nitrogen reduction reaction(NRR)to directly produce NH3 from N_(2) and H_(2)O under ambient conditions has attracted significant attention due to its ecofriendliness.Nevertheless,the electrochemical NRR presents several practical challenges,including sluggish reaction and low selectivity.Here,bi-atom catalysts have been proposed to achieve excellent activity and high selectivity toward the electrochemical NRR by Ma and his co-workers.It could accelerate the kinetics of N_(2)-to-NH_(3) electrochemical conversion and possess better electrochemical NRR selectivity.This work sheds light on the introduction of bi-atom catalysts to enhance the performance of the electrochemical NRR.

Effect of electrochemical reactions droplet metal in direct current on oxygen contamination of submerged arc welding

Agglomerated fluxes with different basicity index designed in laboratory were used to study electrochemical reactions between slag and metal in submerged arc welding under both power polarities. The droplet metal oxygen and nitrogen contents were measured using oxygen-nitrogen instrument in order to analyze indirectly metallurgy electrochemical reactions taking place in cathode and anode of welding arc. The results show that just in the period of droplet growth at the tip of consumable electrode the electrochemical oxygen contamination is produced in the case of direct current electrode positive polarity whereas electrochemical oxygen lost in electrode negative polarity. Furthermore, the results indicate that the basicity index of molten slag has great influence upon electrochemical reaction. With basicity index increasing, the effect of oxygen transferring resulted from electrochemistry becomes more evident for reacting dynamics depended on ion characteristics of molten slag. The effect of basicity index on metal-slag electrochemical reaction is contrary to traditional thermo-chemical reaction and therefore it is necessary to be considered as a metallurgy factor.

CHRONOABSORPTOMETRY FOR THE DETERMINATION OF KINETIC PARAMETERS OF ELECTRON TRANSFER REACTIONS USING LONG-OPTICAL-PATH ELECTROCHEMICAL CELL

A single potential step chronoabsorptometric method for the determination of ki- netic parameters of simple quasi-reversible reactions is described.It is verified by determining the kinetic parameters for the electroreduction of ferricyanide.A long-optical-path electro- chemical cell with a plug-in electrode is used.The thickness of solution layer is 0.55 mm

Electrochemical Determination of Rate Constants for Reactions of OH and its Application in the Evaluation of Anti-Oxidant Actions of Rheum

A single-sweep oscillopolarographic procedure is descrital which allows detethenahon of rateconstants for reachons of oH. For a wide range of compounds, the results fit well with rate constantspreviously obtained with other methods. Rate constants for reactions of six kinds of active compoundscontalned in rheum, a tradihonal Chinese herb, have been deteboned by this method. Rcationmechanism ha5 also been discussed.

Zeolite-mediated hybrid Cu^(+)/Cu~0 interface for electrochemical nitrate reduction to ammonia

The electrocatalytic conversion of reactive nitrogen species to ammonia is a promising strategy for efficient NH_(3) synthesis.In this study,we reveal that the hybrid Cu^(+)/Cu~0 interface is catalytically active for electrochemical ammonia synthesis from nitrate reduction.To maintain the hybrid Cu^(+)/Cu~0 state at negative reaction potentials,hydrophilic zeolite is used to modify Cu/Cu_(2)O electrocatalyst,which demonstrates an impressive NH_(3) production rate of 41.65 mg h^(-1) cm^(-2)with ~100% Faradaic efficiency of ammonia synthesis at-0.6 V vs.RHE.In-situ Raman spectroscopy unveil the high activity originates from the zeolite reconstruction at the electrode–electrolyte interface,which protects the valence state of Cu~0/Cu^(+) site under negative potential and promotes electrochemical activity towards NH_(3) synthesis.

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.

Bimetallic In_(2)O_(3)/Bi_(2)O_(3) Catalysts Enable Highly Selective CO_(2) Electroreduction to Formate within Ultra-Broad Potential Windows

CO_(2)electrochemical reduction reaction(CO_(2)RR)to formate is a hopeful pathway for reducing CO_(2)and producing high-value chemicals,which needs highly selective catalysts with ultra-broad potential windows to meet the industrial demands.Herein,the nanorod-like bimetallic ln_(2)O_(3)/Bi_(2)O_(3)catalysts were successfully synthesized by pyrolysis of bimetallic InBi-MOF precursors.The abundant oxygen vacancies generated from the lattice mismatch of Bi_(2)O_(3)and ln_(2)O_(3)reduced the activation energy of CO_(2)to*CO_(2)·^(-)and improved the selectivity of*CO_(2)·^(-)to formate simultaneously.Meanwhile,the carbon skeleton derived from the pyrolysis of organic framework of InBi-MOF provided a conductive network to accelerate the electrons transmission.The catalyst exhibited an ultra-broad applied potential window of 1200 mV(from-0.4 to-1.6 V vs RHE),relativistic high Faradaic efficiency of formate(99.92%)and satisfactory stability after 30 h.The in situ FT-IR experiment and DFT calculation verified that the abundant oxygen vacancies on the surface of catalysts can easily absorb CO_(2)molecules,and oxygen vacancy path is dominant pathway.This work provides a convenient method to construct high-performance bimetallic catalysts for the industrial application of CO_(2)RR.

Influence of freezing rate on microstructure and electrochemical properties of Mg-2%Ga alloys

Equilibrium freezing curve of Mg-2%Ga （mass fraction） alloy was calculated by CALPHALD method. Microstructures of the melted Mg-2%Ga alloys solidified by iron and copper moulds, respectively, were investigated using OM and SEM. Electrochemical properties of the Mg-2%Ga alloys with different freezing rates were measured by galvanostatic, potentiodynamic and electrochemical impedance spectroscopy tests. The results show that solidification by copper mould leads to intergranular MgsGa2 compounds with small size and large number density. Less adsorbent of Mg^＋ and oxide corrosion products occur on the surface of the Mg-2%Ga alloys solidified by copper mould, producing lower corrosion current density of 1.8×10^-5 mA/cm^2. In the galvanostatic tests with 100 mA/cm^2 current density, more negative stable potential of-1.604 V exists in the Mg-2%Ga alloys solidified by iron mould due to the lower freezing rate, which leads to smaller inductive and capacity time constants as well as shorter activity time and better electrochemical activity.

Exploring nitrogen reduction reaction mechanisms in electrocatalytic ammonia synthesis:A comprehensive review

The electrochemical nitrogen reduction reaction(eNRR)holds significant promise as a sustainable alternative to the conventional large-scale Haber Bosch process,offering a carbon footprint-free approach for ammonia synthesis.While the process is thermodynamically feasible at ambient temperature and pressure,challenges such as the competing hydrogen evolution reaction,low nitrogen solubility in electrolytes,and the activation of inert dinitrogen(N_(2))gas adversely affect the performance of ammonia production.These hurdles result in low Faradaic efficiency and low ammonia production rate,which pose obstacles to the commercialisation of the process.Researchers have been actively designing and proposing various electrocatalysts to address these issues,but challenges still need to be resolved.A key strategy in electrocatalyst design lies in understanding the underlying mechanisms that govern the success or failure of the electrocatalyst in driving the electrochemical reaction.Through mechanistic studies,we gain valuable insights into the factors affecting the reaction,enabling us to propose optimised designs to overcome the barriers.This review aims to provide a comprehensive understanding of the various mechanisms involved in eNRR on the electrocatalyst surface.It delves into the various mechanisms such as dissociative,associative,Mars-van Krevelen,lithium-mediated nitrogen reduction and surface hydrogenation mechanisms of nitrogen reduction.By unravelling the intricacies of eNRR mechanisms and exploring promising avenues,we can pave the way for more efficient and commercially viable ammonia synthesis through this sustainable electrochemical process by designing an efficient electrocatalyst.

Synergistic promotion of particulate matter reduction and production performance via adjusting electrochemical reactions in the zinc electrolysis industry

Heavy particulate matter (PM) pollution and high energy consumption are the bottlenecks of hydrometallurgy, especially in the electrolysis process. Therefore, an urgent need is to explore PM reduction methods with production performance co-benefits. This study presents three PM reduction methods based on controlling operating parameters, i.e., lowering electrolyte temperature, H2SO4 concentration, and current density of the cathode. The optimized conditions were also investigated using the response surface methodology to balance the PM reduction effect and Zn production. The results showed that lowering electrolyte temperature is the most efficient, with an 89.0% reduction in the PM generation flux (GFPM). Reducing H2SO4 concentration led to the minimum side effects on the current efficiency of Zn deposition (CEZn) or power consumption (PC). With the premise of non-deteriorating CEZn and PC, GFPM can be reduced by 86.3% at the optimal condition (electrolyte temperature = 295 K, H2SO4 = 110 g/L, current density = 373 A/m^(2)). In addition, the reduction mechanism was elucidated by comprehensively analyzing bubble characteristics, electrochemical reactions, and surface tension. Results showed that lower electrolyte temperature inhibited the oxygen evolution reaction (OER) and compressed gas volume. Lower H2SO4 concentration inhibited the hydrogen evolution reaction (HER) and reduced electrolyte surface tension. Lower current density inhibited both OER and HER by decreasing the reaction current. The inhibited gas evolutions reduced the microbubbles’ number and size, thereby reducing GFPM. These results may provide energy-efficient PM reduction methods and theoretical hints of exploring cleaner PM reduction approaches for industrial electrolysis.

Interface and energy band manipulation of Bi2O3-Bi2S3 electrode enabling advanced magnesium-ion storage

Rechargeable magnesium-ion(Mg-ion)batteries have attracted wide attention for energy storage.However,magnesium anode is still limited by the irreversible Mg plating/stripping procedure.Herein,a well-designed binary Bi_(2)O_(3)-Bi_(2)S_(3)(BO-BS)heterostructure is fulfilled by virtue of the cooperative interface and energy band engineering targeted fast Mg-ion storage.The built-in electronic field resulting from the asymmetrical electron distribution at the interface of electron-rich S center at Bi_(2)S_(3) side and electron-poor O center at Bi_(2)O_(3) side effectively accelerates the electrochemical reaction kinetics in the Mg-ion battery system.Moreover,the as-designed heterogenous interface also benefits to maintaining the electrode integrity.With these advantages,the BO-BS electrode displays a remarkable capacity of 150.36 mAh g^(−1) at 0.67 A g^(-1) and a superior cycling stability.This investigation would offer novel insights into the rational design of functional heterogenous electrode materials targeted the fast reaction kinetics for energy storage systems.

Effects of stress dependent electrochemical reaction on voltage hysteresis of lithium ion batteries

Intercalation of lithium ions into the electrodes of lithium ion batteries is affected by the stress of active materials, leading to energy dissipation and stress dependent voltage hysteresis. A reaction-diffusion-stress coupling model is established to investigate the stress effects under galvanostatic and potentiostatic operations. It is found from simulations that the stress hysteresis contributes to the voltage hysteresis and leads to the energy dissipation. In addition, the stress induced voltage hysteresis is small in low rate galvanostatic operations but extraordinarily significant in high rate cases. In potentiostatic operations, the stresses and stress induced overpotentials increase to a peak value very soon after the operation commences and decays all the left time. Therefore,a combined charge-discharge operation is suggested, i.e., first the galvanostatic one and then the potentiostatic one. This combined operation can not only avoid the extreme stress during operations so as to prevent electrodes from failure but also reduce the voltage hysteresis and energy dissipation due to stress effects.

Recent advances and strategies in the stabilization of single-atom catalysts for electrochemical applications

Owing to the rapidly increasing consumption of fossil fuels,finding clean and reliable new energy sources is of the utmost importance.Thus,developing highly efficient and low-cost catalysts for electrochemical reactions in energy conversion devices is crucial.Single-atom catalysts(SACs)with maximum metal atom utilization efficiency and superior catalytic performance have attracted significant attention,especially for electrochemical reactions.However,because of the highly unsaturated coordination environment,the stability of SACs can be a challenge for practical applications.In this review,we will summarize the strategies to increase the stability of SACs and synthesizing stable SACs,as well as the application of SACs in electrochemical reactions.Finally,we offer a perspective on the development of advanced SACs through rational design and a deeper understanding of SACs with the help of in situ or operando techniques in electrochemical reactions.

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.