Synthesis Of Bimetallic Hydroxide/oxide Catalysts And Their Electrochemical Performance For Electrolytic Water Splitting

Hydrogen energy is regarded as the cleanest energy source.Hydrogen production by electrolysis of water is a promising green hydrogen production technology.Alkaline water splitting technology is currently being used on a global commercial scale.Compared with solid oxide electrolysis and proton exchange membrane electrolysis,alkaline electrolysis of water requires higher voltage and more energy consumption,and therefore requires oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?catalysts with excellent catalytic performance.At present,the application of transition metal compounds which are abundant and cheap on earth in alkaline water electrolysis has been widely studied.Among these materials,transition metal hydroxides and oxides are considered to be the best choice for hydrolytic electrocatalysts in alkaline electrolytes,but their OER and HER catalytic properties remain to be improved.Since transition metal hydroxides and oxides have poor conductivity,in situ growth of catalytic active components on three-dimensional?3D?conductive substrate can be selected to avoid the use of binder and improve the conductivity of catalysts.The components of the transition hydroxides have a great influence on their OER performance.Transition metal oxides,which are considered to be HER inert,can enhance their HER catalytic activity by doping elements or loading other highly active HER catalytic components.The specific work and research results of this paper are as follows:?1?In chapter 3,the Fe-Ni bimetallic foam was used as not only Fe and Ni sources but also conductive substrate to construct Fe-Ni hydroxide nanosheets network on Fe-Ni bimetal foam by an easy,low-cost and efficient approach.The ratio of Ni/Fe elements played the important role in realizing the optimal catalytic activities for OER and HER.The resultant electrode of FN LDH/FNF-60 possessed low overpotential of 261 m V to reach 10 m A cm^-2,low Tafel slope(85.5 m V dec^-1),and superior long-term stability(remaining 10 m A cm^-2 for 14 h with no attenuation)toward OER in 1.0 M KOH.Moreover,an alkaline water electrolyzer constructed with the FN LDH/FNF-60 as anode and Ni?OH?₂/FNF-25 as cathode,respectively,displayed superior electrolysis performance(providing 10 m A cm^-2 under 1.62 V)and long-term durability compared with the RuO₂ and 20 wt.%Pt/C.?2?In chapter 4,3D interconnected ultrathin Ni doped Co₃O₄ nanosheet arrays?Ni-Co₃O₄NS\NF?were grown on the surface of Ni foam by a facile one-pot chemical bath deposition process under low temperature??90°C?and atmospheric condition.This synthesis approach was very green,low-cost and easily scaled up with the size of substrate and was also common method for synthesizing other Ni doped metal oxide electrocatalysts,such as Ni-Mn₃O₄NS\NF and Ni-Fe₂O₃NP\NF.The as-prepared Ni-Co₃O₄NS\NF exhibited excellent OER and HER catalytic activities in 1.0 M KOH,due to its high active surface area,interconnected nanosheets array,good conductivity and fast charge transport in electrolysis process.Subsequently,a water splitting electrolyzer based on the easy-prepared Ni-Co₃O₄NS\NF afforded a current density of 90.8 m A cm^–2 under a cell voltage of 2.0 V,which was about 5-times than industrial Ni foam.Furthermore,we also demonstrate that it could be a promising candidate in overall water splitting devices for large scale solar-to-hydrogen generation.?3?In chapter 5,abundant Ru nanoclusters were loaded on the Co₃O₄ nanowires and the chemical bonding environment of Ru nanoclusters was regulated by controlling reduction reaction.Through characterization,it could be known that chemical environment of the Ru nanoclusters on Co₃O₄nanowires?Ru/Co₃O₄ NWs?were bonded with Ru–O,while Ru–Ru and Ru–Co bonds were detected in Ru/Co NWs.Ru/Co₃O₄ NWs possessed the enhanced HER catalytic activity with an overpotential of 30.96 m V to a current density of 10 m A cm^-2,which was superior to that of Ru/Co NWs?113.29 m V?.Theoretical calculations showed that Ru/Co₃O₄ possessed smaller|?G_H*|than that of Ru/Co,due the regulated electron density states of Ru via O binding.At last,through anodic oxidation of Ru nanoclusters on Co foam?Ru Co/CF?,it was further verified that the introduction of O improved the intrinsic HER activity of Ru in O-Ru Co/CF.Our work provided a possible direction of exploring the catalytic activity of Ru by regulating surrounding bonding and producing the efficient Ru-based HER catalysts.