Design,Synthesis,and Electrochemical Performance Of Integrated Electrode/electrocatalyst

Global studies on renewable energy,such as solar,wind,and hydrogen power,have intensified for the sake of reducing the dependency on fossil fuels in the future energy system and the alarming emissions of greenhouse gases(GHGs).Hydrogen power has been regarded as one of the most potential candidates in the future energy system because of its clean and high efficient merits.And,producing hydrogen power though water electrolysis is the key step to achieve the future hydrogen economy.However,the high cost of energy consumption hinders the widespread use of producing hydrogen via water electrolysis.Based on the theoretical analyses of water electrolysis,this thesis discusses and summarizes the constraints of water electrolysis performance.Focused on the single cathode or anode,this thesis analyzes the optimization approaches of water electrolysis performance from the perspectives of electrode/electrocatalyst configuration,electrocatalyst,and cathode/anode coupling,and subsequently proposes the design concept of integrated electrode/electrocatalyst.The specific works are reflected in the following aspects.(1)High-efficiency non-precious catalysts are important for hydrogen and oxygen evolution reactions(HER and OER).Practical water splitting needs not only intrinsically active catalyst materials but also the maximization of their electrocatalytic capability in a real electrolyzer.Here,we report for the first time a Ni/Ni2P inverse opal architecture fabricated by a surface engineering.The superior HER properties are enabled by the most active crystallographic plane exposure and vertical alignment of Ni2P nanosheets on nickel inverse opal.It requires an overpotential of only 73 mV to drive a HER current density of-20 mA Clcm-2.After doping with Fe,the resulting Fe:Ni/Ni2P inverse electrode shows excellent OER performance with a very low overpotential(285 mV)at a current density of 20,mA cm-2.An alkaline electrolyzer using the two 3D structured electrodes could split water at 20 mA cm-2 with a low voltage of~1.52 V for 100 h.The catalytic activity is even superior to that of noble metal catalyst couple(IrO2-Pt/C).This work provides a surface engineered opal structure to maximize the electrocatalyst properties in the systems with coupled electron transfer and mass transports.(2)Hydrogen production is the key step for the future hydrogen economy.As a promising H2 production route,electrolysis of water suffers from high overpotentials and high energy consumption.This study proposes an N-doped CoP as the novel and effective electrocatalyst for hydrogen evolution reaction(HER)and constructs a coupled system for simultaneous hydrogen and sulfur production.Nitrogen doping lowers the d-band of CoP and weakens the H adsorption on the surface of CoP because of the strong electronegativity of nitrogen as compared to phosphorus.The H adsorption that is close to thermos-neutral states enables the effective electrolysis of the HER.Only—42 mV is required to drive a current density of-10 mA cm-2 for the HER.The oxygen evolution reaction in the anode is replaced by the oxidation reaction of Fe2+,which is regenerated by a coupled H2S absorption reaction.The coupled system could significantly reduce the energy consumption of the HER and recover useful sulfur sources.