Preparation And Electrocatalytic Activities For Water Splitting Of Transition Metal Phosphide Or Hydroxides

Electrochemical water splitting technology is an environmentally friendly and practical approach to generate clean hydrogen for the purpose of storing electric energy.Recently,electrochemical water splitting is coupled with series of electrochemical reactions in which oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?have been regarded as the major heart of these technologies.The major characteristics of these electrocatalysts include high-performance,low-cost,and abundance.Iridium and Ruthenium oxides?Ir O₂ or RuO₂?are the most effective electrocatalysts for OER,while platinum?Pt?is the best HER electrocatalysts.However,while these electrocatalysts are characterized with high-performance,they are very expensive and scarce.Hence,it is very important to explore electrocatalysts,such as transition metal phosphide?TMP?and hydroxide for water splitting with the three abovementioned properties.It has been proven that P atoms in the TMPs play crucial roles for HER by DFT calculations.P atoms with more electronegativity can draw electrons from metal atoms.The negatively charged P act as base to trap positively charged proton during electrochemical HER.The self-activation step of transition metal hydroxide leads a high catalytic performance for OER.In this thesis,a simple way was used to prepare TMP and transition metal hydroxide for electrolysis of water as the follow:1.Here,different from the as-synthesized way of Co_xNi_yP,a low-cost nitrogen-doped carbon embedded with Co_xNi_yP nanosheets supported on Ni foam?Co_xNi_yP@NC/NF?was prepared by low temperature hydrothermal and phosphating method.Since the catalytic was enabled by carbon composites,the stability was improved as naked in ambient atmosphere and the resulted Co_xNi_yP@NC/NF exhibited high hydrogen performance.The Co_xNi_yP@NC/NF exhibited the best performance with an overpotential of 70 mV at-10 mA cm^-2,which was even better than Pt sheet.A current density of 10 mA cm^-2 was achieved at overpotential of 161mV,during the 35 h stability test,the catalytic remained high catalytic activity.What's more,as the ratio of Co:Ni were increased,Co_xNi_yP@NC/NF presented a better HER performance with the cobalt doping.2.In view of the absence of the major characteristics of these electrocatalysts include high-performance,low-cost,and abundance in most work.Here,a simple hydrothermal method was used to produce cost-efficient and high electrocatalytic activity self-supportive electrocatalysts with different morphology of Fe_x Ni_yOOH on the etching galvanized sheet iron?EGSI?for active,stable and low-cost OER/HER catalyst for electrochemical water splitting.These survey results indicate that urea has the most effect to etching EGSI.The electrochemical study indicated that the catalyst can be self-activated during the test,and modest Fe-doping made it achieving better catalytic activity for Fe-doping by controlling the structure.The electrodes had a low overpotential of 228 mV and 237 mV for HER and OER at a current density of 10 mA cm^-2,respectively.It exhibited a low overpotential of 361 mV for HER at the current density of 300 mA cm^-2,and a low overpotential 344 mV for OER at the current density of 600 mA cm^-2.The excellent bifunctional electrocatalysts can be developed both as anode and as cathode of an alkaline electrolyzer which needs a cell voltage of1.69 V to achieve 10 mA cm^-2 current density.The results suggested that the way to prepare Fe_xNi_yOOH makes a lot of sense.3.The porous electrode through the etching of SUS304 stainless steel mesh?ESS?by HCl and Fe³⁺was prepared to make up the lower surface area of EGSI which limited the loading of Fe_xNi_yOOH and limited the improvement of catalytic active for water splitting.Different from Fe_xNi_yOOH/EGSI,through the electrooxidation method,Fe_x Ni_yOOH/ESS had different morphology and exhibited higher OER and HER performance.The results showed that Fe_x Ni_yOOH/ESS had a higher catalytic activity and stability.The porous ESS provided a larger growth area for Fe_xNi_yOOH,and led to a larger active area.The electrodes had a low overpotential of 172 mV and208 mV for HER and OER at a current density of 10 mA cm^-2,respectively.It exhibited a low overpotential of 258 mV for HER at the current density of 300 mA cm^-2,and a low overpotential of 308 mV for OER at the current density of 600 m A cm^-2,and during the 136 h stability test,the catalyst remained high catalytic activity.The excellent bifunctional electrocatalysts can be developed both as anode and as cathode in an alkaline electrolyzer which needs a cell voltage of 1.58 V to achieve 10mA cm^-2 current density.And the results suggest that the Fe_xNi_yOOH/ESS is significant in the development of preparation of cost-effective and high catalytic active electrocatalysts.