Cobalt-,Copper- And Iron-based Electrocatalysts Prepared Via Anion Exchange For Water Splitting

Nowadays,human society is faced with three major problems:insufficient fossil fuels（the discovered oil resources are only sufficient for 40 to 80 years）,climate change,and limited energy storage.combination of water electrolysis technology and renewable energy can efficiently solve these three problems.The water splitting reaction is composed of two half reactions:oxygen evolving reaction（OER）and hydrogen evolving reaction（HER）.Due to the existence of anode/cathode reaction energy barriers and electrolyte resistance in the reaction process,additional overpotentials（η）are often required to drive the reaction,which affects the conversion efficiency of electrical energy to chemical energy.Thus,we designed the following catalysts for the two half reactions to improve the hydrogen production efficiency of the electrocatalytic water splitting.First,a novel hierarchical urchins-like cobalt-copper hydroxide was in situ grown on copper foam（CoCuO_xH_y（S）/CF）via the electrochemical transformation of cobalt-copper sulfides(Co₉S₈-Cu_1.81S)under anodization.When this CoCuO_xH_y（S）/CF anode is used as an OER catalyst,it exhibited a lowηof 274 mV at a current density of 100 mA cm^-2 with a robust durability over a period of 40 h when operating at 10 mA cm^-2.Further detailed investigations implied that the unique nanowires aggregated urchin-like morphology derived from Cu doping and in situ anion exchange process could facilitate the exposure of active sites and accelerate electron transfer.Besides,the incorporation of Cu resulted in an electronic delocalization around Co species,which contributed to reach a high-valent catalytically active Co species and further improved the OER performance.Another important part of the water splitting reaction is HER.We combined the in-situ electrochemical treatment method and the reported phosphoric acid treatment method to design amorphous FeO_xH_y（Pi）nanoparticles as HER catalysts.The FeO_xH_y（Pi）nanoparticles grown in situ showed better HER performance than FePO₄(η=160 mV at j=10 mA cm^-2).Further studies revealed the HER activity of FeO_xH_y（Pi）is mainly derived from its morphology and in-situ growth on Fe foam.In addition,this amorphous FeO_xH_y（Pi）preparation method is inexpensive and the reaction process is simple and easy to scale up.