The Preparation Of Hydrotalcite-based Composites And Their Oxygen Evolution Performance

The rapid consumption of fossil fuels and environmental problems associated with their combustion have stimulated the research and development of renewable energy systems.Electrochemical water splitting is considered a promising approach to obtaining clean fuels(OERs)from renewable sources.Precious metal oxides such as IrOx and RuOx have long been recognized as highly active electrocatalysts for moisture-resolving oxygen.Unfortunately,their scarcity and high cost hamper further large-scale applications.Therefore,there is an urgent need to find alternative catalysts that are low cost and durable to achieve effective OER performance.Hydrotalcites and hydrotalcites(LDHs)are layered double(or poly)metal hydroxides with low cost and simple preparation,but have the disadvantages of insufficient exposure of active sites and poor stability.Therefore,this paper will work on the preparation of hydrotalcite catalysts and their enhanced electrocatalytic properties.(1)Design and performance study of structured LDHs electrocatalysts:The effect of doping of g-C3N4 on the structure and properties of NiFeCr-LDHs was investigated and its oxygen evolution performance was tested.g-C3N4 supported nickel-iron-chromium layered hydroxide(NiFeCr-LDHs/g-C3N4)was synthesized by a simple co-precipitation reaction using strong electrostatic interaction between positively charged Ni2+,Fe3+ and Cr3+ and negatively charged g-C3N4 nanosheets.The effect of g-C3N4 on the structure and catalytic properties of NiFeCr-LDHs was investigated.Experimental analysis shows that g-C3N4 can promote the formation of thinner nanosheets of LDHs.It was found that g-C3N4 has two functions,one promoting and the other inhibiting.The promotion effect comes from the influence of g-C3N4 on NiFeCr-LDHs structure,and the inhibition effect comes from the low conductivity and lack of electrocatalytic activity of g-C3N4.When the weight ratio of g-C3N4 to NiFeCr-LDHs was 5%,the promotion of g-C3N4 was the main and the inhibition effect was negligible.The catalyst displays overpotential of～223 mV at 10 mA cm-2,Tafel slope of 18 mV dec-1 in 1 M KOH solution,and remains stable over 9600s.Its catalytic performance is better than that of pristine NiFeCr-LDHs,bare g-C3N4,and commercial RuO2.Moreover,this work demonstrates the effect of g-C3N4 on the structure of the LDHs formation process and can provide a reference for the design of high efficiency OER catalysts.(2)Preparation of metal phosphide based on hydrotalcite precursor and investigation of its oxygen evolution performance:Firstly,NiFeZn-LDHs/NF was prepared by hydrothermal method,and metal phosphide NiFeZnP-0.5/NF was synthesized by using sodium hypophosphite as reducing agent.Its oxygen evolution performance was tested.The results show that the prepared catalyst NiFeZnP-0.5/NF has a 3D layered structure,the active site can reach the maximum exposure,and the electrocatalytic activity is better.At the same time,the doping of Zn2+increases the active site of the electrocatalyst.The catalytic activity of oxygen evolution of water has been greatly improved.It has a low overpotential of～136mv at 10mA cm-2,a low overpotential of～201mV at 100 mA cm-2,and a lower Tafel slope of～35mV dec-1 for stability testing of the catalyst.It was found that at a current density of 100 mA cm-2,the NiZnFeP-0.5/NF electrode remained stable at 6 hours,hardly decreased,and the performance was superior to that of commercial RuO2.