Research On Nickel-based Bifunctional Catalyst Supported By Self-supporting Expanded Graphite Sheet

With the increasing energy crisis and environmental pollution problems,hydrogen energy produced by overall water splitting has been considered as the clean energy with the greatest development potential in the 21st century due to its high energy density,non-pollution and abundant reserves.At present,Pt/C and RuO₂ are used as commercial catalysts for hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,respectively,but high price limits their wide range of applications.Therefore,the preparation of low-cost catalyst with excellent catalytic activity and stability is of great significance for the conversion of renewable energy and the expansion of storage technology.In this paper,flexible graphite sheet was used as the raw material and the surface was partially expanded by electrochemical intercalation in 1 M KOH to obtain self-supporting expanded graphite sheet?SSEGS?.SSEGS could be used as an ideal three-dimensional support material,in which the expanded part could load much active material and provide an efficient conductive path,and the unexpanded part could act as the current collector to avoid the use of additional binder.Then Ni-P and Ni-Cu-P alloy were deposited on SSEGS by electroless plating to obtain Ni-P/SSEGS and Ni-Cu-P/SSEGS catalysts.Among them,Ni-Cu-P/SSEGS material exhibited better HER and OER performance than Ni-P/SSEGS in1 M KOH.The overpotentials of 75 and 300 mV were required for HER and OER to reach10 mA/cm² in 1 M KOH,respectively.In addition,the Ni-Cu-P/SSEGS catalyst also showed superior stability.In order to further improve the OER catalytic activity,the NiFe hydroxide was deposited on the surface of Ni-P/SSEGS and Ni-Cu-P/SSEGS by electrodeposition to obtain NiFe-OH/Ni-P/SSEGS and Ni Fe-OH/Ni-Cu-P/SSEGS composite catalysts.The electrochemical results showed that the NiFe-OH/Ni-Cu-P/SSEGS composite catalyst exhibited excellent bifunctional catalytic activity than NiFe-OH/Ni-P/SSEGS.The NiFe-OH/Ni-Cu-P/SSEGS composite catalyst just required the overpotentials of 223 and 276 mV to reach 100 mA/cm² for HER and OER in 1 M KOH,respectively.In addition,the NiFe-OH/Ni-Cu-P/SSEGS material was also used as anode and cathode to constrcuct a two-electrode system.The overall water splitting electrochemical results showed that the two-electrode system just required a low potential of 1.56 V to achieve 10 mA/cm² and also had excellent stability.