Preparation Of Transition Metal Composite Nanomaterials And Electroatalytic Performance For Water Splitting

The increased consumption of fossil fuel has greatly promoted the development of society,accompanied by serious energy shortages and environmental pollution at the same time,which have prompted researchers to seek eco-friendly renewable energy to replace fossil fuels.In view of the high calorific value of combustion and no pollutant emissions to the environment during combustion,hydrogen energy is considered to be the most promising alternative energy source for fossil fuels.Hydrogen production by electrolysis of water is the most promising high-efficiency green technology hydrogen production that can meet the needs of future energy.It can convert electrical energy(intermittent renewable energy,such as solar,wind and ocean energy)into hydrogen energy.The electrolysis water reaction consists of two half reactions,namely the cathode hydrogen evolution reaction(HER)and the anode oxygen evolution reaction(OER).Due to the dynamic barriers of these two half-reactions,the electrochemical water splitting requires a higher applied voltage.Therefore,it is necessary to develop a highly active electrocatalyst for the hydrogen evolution reaction and the oxygen evolution reaction as soon as possible to overcome the slow kinetics and higher overpotential,and to further accelerate the rate of the hydrogen production reaction.According to reports,Pt,Pt/C,Ir O₂and Ru O₂are currently commercial electrocatalysts for hydrogen evolution reaction and oxygen evolution reaction.However,these precious metal catalysts are scarce and expensive,and therefore cannot meet the demand for large-scale hydrogen production.To solve this problem,researchers are committed to developing high-performance and low-cost electrocatalysts.Transition metal compounds(including oxides,phosphides,sulfides,selenides,nitrides,etc.),due to their abundant resources,low cost and a large number of active sites,are considered as potential electrocatalysts for hydrogen evolution and oxygen evolution.Based on the above considerations,this article takes transition metal composite materials as the main research object,and combines dealloying and other methods as the main preparation methods.By increasing the types of transition metals,a series of transition metal composite materials have been prepared and used as electrocatalysts for electrochemical water splitting.The main content of the paper is as follows:1.Preparation of Co_0.85Se nanosheets and electroatalytic performance for hydrogen evolution reactionThe flexible and nonprecious Co metal plate was optioned as the source conductive scaffold and then electrodepositing Zn on Co plate was first conducted followed by annealing in ar atmosphere to obtain Co Zn alloy surface layer.And then,selectively etching zinc atoms from Co Zn@Co in ammonia solution generated Co₃O₄nanosheets grown on Co plate(Co₃O₄NSs@Co)with large surface area.Finally,in situ topotactic conversion from Co₃O₄NSs@Co to the Co_0.85Se nanosheets grown on Co plate(Co_0.85Se NSs@Co)was simply achieved by the hydrothermal selenization along with the good structural inheritation.The whole preparation is highly reproducible with absolute yield.Owing to the specific integral architecture composed of conductive substrate and 2D nanosheet subunits,Co_0.85Se NSs@Co nanosheets shows excellent electrocatalytic activity,good catalytic durability and excellent structural stability for hydrogen evolution reactions in wide range of p H electrolytes.The proposed preparation strategy is highly versatile and flexible,which can be extended to design some other single and composited electocatalysts.2.Preparation of high-entropy nickel-cobalt composite phosphorus oxides and electroatalytic performance for oxygen evolution reactionMelting Ni,Co,Fe,and Al in different proportions are smelted in a vacuum electric arc furnace,and the strip is spin-quenched in an argon atmosphere to obtain Ni Co Fe Al alloy strips with different proportions.Selectively partially corrode aluminum atoms in sodium hydroxide solution to adjust the morphology of the quaternary oxide precursor,and then perform gas phase phosphating to successfully prepare high-entropy Ni Co Fe Al PO_xnanosheets with controllable morphology and different proportions,composed of rich open channels and interlinking two dimensional nanosheet arrays are successfully prepared.Benefiting from the synergy between sufficient active sites of multiple elements and smooth mass transfer,as well as the unique catalytic properties of high-entropy compounds,compared with other electrocatalysts,the Ni₇Co₂Fe Al PO_xelectrocatalyst exhibits excellent electrocatalytic performance and satisfactory long-term durability for oxygen evolution reactions.The low cost of the transition metal composite and the easy mass production of the preparation method make it possible to be used for commerical water splitting.