Unveiling the geometric site dependent activity of spinel Co_(3)O_(4)for electrocatalytic chlorine evolution reaction

Spinel cobalt oxide(Co_(3)O_(4)),consisting of tetrahedral Co^(2+)(CoTd)and octahedral Co^(3+)(CoOh),is considered as promising earth-abundant electrocatalyst for chlorine evolution reaction(CER).Identifying the catalytic contribution of geometric Co site in the electrocatalytic CER plays a pivotal role to precisely modulate electronic configuration of active Co sites to boost CER.Herein,combining density functional theory calculations and experiment results assisted with operando analysis,we found that the Co_(Oh) site acts as the main active site for CER in spinel Co_(3)O_(4),which shows better Cl^(-)adsorption and more moderate intermediate adsorption toward CER than CoTd site,and does not undergo redox transition under CER condition at applied potentials.Guided by above findings,the oxygen vacancies were further introduced into the Co_(3)O_(4) to precisely manipulate the electronic configuration of Co_(Oh) to boost Cl^(-)adsorption and optimize the reaction path of CER and thus to enhance the intrinsic CER activity significantly.Our work figures out the importance of geometric configuration dependent CER activity,shedding light on the rational design of advanced electrocatalysts from geometric configuration optimization at the atomic level.

XPS and Cyclic Voltammetric Surface Characterization of Terbium Oxide Electrocatalysts

The surface characteristics and electrochemical behaviors of Tb 4O 7 layers deposited on graphite by thermal decomposition were investigated by means of XPS and cyclic voltammetry at 700 ℃ in NaCl KCl melts. XPS analysis indicates that thermal decomposition products are mainly non stoichiometric and defective structurally oxide. Cyclic polarization on oxide electrode reflects the specific adsorption of Cl - and structural modification of oxide surface. Analysis based on the features of the voltammograms reveals the redox behaviors of Tb oxide layer with different valency states and its correlation to electrocatalytic active. The variation of voltammetric charge was used to characterize the affection of temperature, measure the electrochemical active surface area and monitor the modification of active surface.

Study of engineering electronic structure modulated non-noble metal oxides for scaled-up alkaline blend seawater splitting

Scaled-up industrial water electrolysis equipment that can be used with abundant seawater is key for affordable hydrogen production.The search for highly stable,dynamic,and economical electrocatalysts could have a significant impact on hydrogen commercialization.Herein,we prepared energy-efficient,scalable,and engineering electronic structure modulated Mn-Ni bimetal oxides(Mn_(0.25)Ni_(0.75)O)through simple hydrothermal followed by calcination method.As-optimized Mn_(0.25)Ni_(0.75)O displayed enhanced oxygen and hydrogen evolution reaction(OER and HER)performance with overpotentials of 266 and115 mV at current densities of 10 mA cm^(-2)in alkaline KOH added seawater electrolyte solution.Additionally,Mn-Ni oxide catalytic benefits were attributed to the calculated electronic configurations and Gibbs free energy for OER,and HER values were estimated using first principles calculations.In real-time practical application,we mimicked industrial operating conditions with modified seawater electrolysis using Mn_(0.25)Ni_(0.75)O‖Mn_(0.25)Ni_(0.75)O under various temperature conditions,which performs superior to the commercial IrO_(2)‖Pt-C couple.These findings demonstrate an inexpensive and facile technique for feasible large-scale hydrogen production.

RuO_(2)/TiO_(2)/MXene with multi-heterojunctions coating on carbon cloth for high-activity chlorine evolution reaction at large current densities

The chlorine evolution reaction(CER)is a crucial step in the production of chlorine gas and active chlorine by chlor-alkali electrolysis.Currently,the endeavor to fabricate electrodes capable of yielding high current density at minimal overpotential remains a central challenge in advancing the realm of chlorine evolution reactions.Here,we grow TiO_(2)and RuO_(2)on MXene@carbon cloth(CC)through the favorable affinity and induced deposition effect between the surface functional groups of MXene and the metal.A self-supported electrode(RuTiO_(2)/MXene@CC)with strong binding at the electrocatalyst-support interface and weak adhesion at electrocatalyst-bubble interface is constructed.The RuTiO_(2)/MXene@CC can reduce the electron density of RuO_(2)by regulating the electron redistribution at the heterogeneous interface,thus enhancing the adsorption of Cl−.RuTiO_(2)/MXene@CC could achieve a high current density of 1000 mA·cm^(−2)at a small overpotential of 220 mV,superior to commercial dimensionally stable anodes(DSA).This study provides a new strategy for constructing efficient CER catalysts at high current density.

Stability of dimensionally stable anode for chlorine evolution reaction

Chlorine(Cl2)is one of the most important chemicals produced by the electrolysis of brine solutions and is a key raw material for many areas of industrial chemistry.For nearly half a century,dimensionally stable anode(DSA)made from a mixture of RuO_(2) and TiO_(2) solid oxides coated on Ti substrate has been the most widely used electrode for chlorine evolution reaction(CER).In harsh operating environments,the stability of DSAs remains a major challenge greatly affecting their lifetime.The deactivation of DSAs significantly increases the cost of the chlor-alkali industry due to the corrosion of Ru and the formation of the passivation layer TiO_(2).Therefore,it is urgent to develop catalysts with higher activity and stability,which requires a thorough understanding of the deactivation mechanism of DSA catalysts.This paper reviews existing references on the deactivation mechanisms of DSA catalysts,including both experimental and theoretical studies.Studies on how CER selectivity affects electrode stability are also discussed.Furthermore,studies on the effects of the preparation process,elemental composition,and surface/interface structures on the DSA stability and corresponding improvement strategies are summarized.The development of other non-DSA-type catalysts with comparable stability is also reviewed,and future opportunities in this exciting field are also outlined.

Recent progress in transition-metal-oxide-based electrocatalysts for the oxygen evolution reaction in natural seawater splitting: A critical review

Direct electrolytic splitting of seawater for the production of H2 using ocean energy is a promising technology that can help achieve carbon neutrality.However,owing to the high concentrations of chlorine ions in seawater,the chlorine evolution reaction always competes with the oxygen evolution reaction(OER)at the anode,and chloride corrosion occurs on both the anode and cathode.Thus,effective electrocatalysts with high selectivity toward the OER and excellent resistance to chloride corrosion should be developed.In this critical review,we focus on the prospects of state-of-the-art metal-oxide electrocatalysts,including noble metal oxides,non-noble metal oxides and their compounds,and spinel-and perovskite-type oxides,for seawater splitting.We elucidate their chemical properties,excellent OER selectivity,outstanding anti-chlorine-corrosion performance,and reaction mechanisms.In particular,we review metal oxides that operate at high current densities,near industrial application levels,based on special catalyst design strategies.

Non-noble-metal electrocatalysts for oxygen evolution reaction toward seawater splitting: A review

The direct electrolytic splitting of abundant seawater instead of scarce freshwater is an ideal strategy for producing clean and renewable hydrogen(H 2)fuels.The oxygen evolution reaction(OER)is a vital half-reaction that occurs during electrochemical seawater splitting.However,OER suffers from sluggish four-electron transfer kinetics and competitive chlorine evolution reactions in seawater.Noble metal-based catalysts such as IrO_(2) and RuO_(2) are considered to have state-of-the-art OER electrocatalytic activity,but the low reserves and high prices of these noble metals significantly limit their large-scale application.Recently,efforts have been made to explore efficient,robust,and anti-chlorine-corrosion non-noble-metal OER electrocatalysts for seawater splitting such as oxides,hydroxides,phosphides,nitrides,chalcogenides,alloys,and composites.An in-depth understanding of the fundamentals of seawater electrolysis and the design principle of electrode materials is important for promoting seawater-splitting technology.In this review,we first introduce fundamental reactions in seawater electrolytes.Subsequently,construction strategies for OER electrocatalysts for seawater splitting are introduced.Finally,present challenges and perspectives regarding non-noble-metal OER electrocatalysts for commercial H 2 production by seawater splitting are discussed.

N-doped carbon dots coupled NiFe-LDH hybrids for robust electrocatalytic alkaline water and seawater oxidation

Electrolysis of seawater offers a highly promising and sustainable route to attain carbon-neutral hydrogen energy without demanding on high-purity water resource.However,it is severely limited by the undesirable chlorine oxidation reaction(ClOR)on the anode and the releasing toxic chlorine species,inducing anode corrosion and multiple pollutions to reduce the efficiency and sustainability of this technology.The effective way is to limit the overpotential of oxygen evolution reaction(OER)below 480 mV and thus suppress the ClOR.Herein,we demonstrate that nitrogen-doped carbon dots strongly coupled NiFe layered double hydroxide nanosheet arrays on Ni foam(N-CDs/NiFe-LDH/NF)can efficiently facilitate OER with an ultralow overpotential of 260 mV to deliver the geometric current density of 100 mA·cm^(−2)and a Tafel slope of as low as 43.4 mV·dec−1 in 1.0 M KOH.More importantly,the N-CDs/NiFe-LDH/NF electrode at 100 mA·cm^(−2)shows overpotentials of 285 and 273 mV,respectively,by utilizing 1.0 M KOH with 0.5 M NaCl and 1.0 M KOH with 1.0 M NaCl as the simulated seawater,well avoid triggering ClOR.Notably,despite the complex environment of real seawater,N-CDs/NiFe-LDH/NF still effectively promotes alkaline seawater(1.0 M KOH+seawater)electrolysis with a lifetime longer than 50 and 20 h,respectively,in 1.0 M KOH and alkaline seawater electrolytes.The investigation result reveals that M–N–C bonding generated between N-CDs and NiFe-LDH intrinsically optimizes the charge transfer efficiency,further promoting the OER kinetics.

Electrocatalytic seawater splitting for hydrogen production:Recent progress and future prospects

Earth-abundant seawater resource has become an attractive candidate to produce hydrogen from electrolysis,which is of great significance to realize hydrogen economy and carbon neutrality.Nonetheless,developing highly active and stable electrocatalysts to meet the needs of highly effective seawater splitting is still challenging for the sluggish oxygen evolution dynamics and the existed competitive reaction of chlorine evolution reaction(CER).To this end,some newly-developed electrocatalysts with superior performance,such as noble metals,alloy,transition metals,oxides,carbides,nitrides,phosphides,and so on,have been synthesized for the seawater splitting in recent years.This review starts from the historical background and fundamental mechanisms,and summarizes the most recent progress in the development of seawater electrolysis technologies.Some existing issues in the process of seawater electrolysis are enumerated and the corresponded solutions are presented.The future of hydrogen production from seawater electrolysis,especially the design and synthesis of novel catalysts for seawater electrolysis,is prospected.

Advancements in Seawater Electrolysis:Progressing from Fundamental Research to Applied Electrolyzer Application

Seawater electrolysis(SWE)provides a promising and efficient pathway to produce green hydrogen.However,the current SWE technology confronts a lot of challenges,such as the sluggish reaction kinetics on the anode side,and a lot of impurities and ions in seawater that poison the active sites of the catalyst and block membrane pores.In addition,the existence of chloride ions(Cl−)in seawater will strongly compete with oxygen evolution reaction(OER)by the chlorine oxidation/evolution reaction(ClOR/ClER)on the anode side as a result of the extremely similar thermodynamic potentials.Thus,to move SWE much closer to commercialization,it is highly desirable to enhance not only the activity of electrocatalysts but also the selectivity and stability of efficient OER to restrain ClOR/ClER.At the same time,the additive of electrolytes and the unique structural design of the electrolyzer also promote the development of SWE.In this review,the fundamental mechanisms for SWE and water electrolysis are first introduced and compared.Then,the design principles of efficient catalysts,electrolytes,surface/interface engineering,and novelty reaction device are critically,comprehensively summarized and analyzed.Finally,perspectives,challenges,and opportunities to develop and boost SWE technologies are proposed.

A facile synthesis of cyano-chlorins related to chlorophyll from formyl (pyro)-pheophorbide-a by a tandem transformation of the aldehyde into a nitrile group

A facile synthesis for cyanochlorin related to chlorophyll from a formyl-substituted chlorin, by the oxidation of methyl （pyro）pheophorbide-a, was accomplished. These readily available chlorin aldehydes were assembled together with hydroxylamine hydrochloride in a tandem process to produce the corresponding chlorin nitriles in moderate to good yields. The formation of chlorin nitrile was discussed and a possible mechanism for the corresponding cyanation reaction was tentatively proposed.