Design Of Transition Metal-based Nanocatalyst Electrodes And Study On The Electrocatalytic Performance Of Water Electrolysis And CO₂ Reduction

The excessive consumption of fossil fuels has produced increasingly severe energy crises,global warming and pollution,bringing the enormous challenge to the sustainable development of human society.Therefore,the rapid development of green and renewable energy systems is urgent need.The electrocatalytic energy conversion and storage technologies(such as,electrolysis of water to produce hydrogen,electrochemical reduction of CO2 to produce chemical fuels)have attracted widespread attention due to the high conversion efficiency,simple equipment and environmental friendliness.The catalytic electrode is the core component that determines the energy conversion efficiency of the electrocatalytic process.Therefore,how to design an efficient and stable catalytic electrode is a crucial factor restricting the development of modern electrocatalytic technology.Traditional noble metal(Ir,Pt,Ru,Pd and Au)catalytic electrodes make modern electrocatalytic technology more expensive and lower energy conversion efficiency due to limited reserves,high prices and slow catalytic kinetic processes.Hence,to promote the widespread application of electrocatalysis technology,it is necessary to design catalytic electrodes with higher activity,stability and cheapness.Based on the current research status and needs,this thesis designs and studies some transition metal-based catalytic electrodes by regulating the composition,physical structure and electronic structure,at the same time,the structure-activity relationship is revealed.The main research content focuses on the following four aspects:1.The ternary NiFeV LDHs array growing on nickel foam was synthesized by a simple one-step hydrothermal method,which possessed excellent OER catalytic activity.After introducing vanadium into the NiFe LDHs laminate,the laminate electronic structure of NiFe LDHs was optimized,favoring the adsorption and desorption energy of the OER intermediates at the active site,reducing the reaction resistance and improving OER intrinsic activity of the catalyst.Meanwhile,the doping of vanadium could narrow the bandgap between the conduction band and the valence band,increasing the conductivity of the material,accelerating the electron transfer in the catalytic process.Thus,this ternary NiFeV LDHs array only need an overpotential of 195 mV to reach a current density of 20 mA/cm2.There was only 2%decay in current density after 18 hours constant voltage stability test.2.A mildly controlled synthesis method was used to combine CoFe LDHs with Ru ion to fabricate the monoatomic Ru OER catalyst.The strong electron coupling between CoFe LDHs and single atom Ru was used to optimize the electronic structure of the catalytic material,improving the catalytic activity.In-situ X-ray absorption analysis and Density Functional Theory simulation showed that single-atom Ru was the active center for OER catalysis.At the same time,the in-situ X-ray absorption test results confirmed that the CoFe LDHs substrate undergone structural contraction during the OER process.The changed structure could be used as an electron donor to transfer some electrons to monoatomic Ru avoiding the valence of monoatomic Ru increasing to greater than+4,thus,ensuring the stability of monoatomic Ru.3.A compound of amorphous RuSx and graphene oxide(GO)was fabricated by hydrothermal method,which possessed Pt-like activity towards HER in acidic,neutral and alkaline environments.RuSx nanoparticles were evenly distributed on GO.We found that the amorphous RuSx nanomaterial could well tolerate local pH changes around the surface of the catalytic electrode during the catalytic process,ensuring the durability of catalytic activity.The X-ray absorption spectrum showed that the distance between the two Ru atoms in the amorphous RuSx was relatively long,which could make sure the HER was carried out according to the single active site catalytic mechanism(Volmer-Heyrovsky).At the same time,theoretical simulation calculations showed that this RuSx material had similar H adsorption capacity to platinum:neither strong nor weak,conforming to Sabatier principle.The RuSx based material was an excellent HER catalyst.4.An O2-tolerant CO2 reduction electrode was designed.It consisted of a gas separation layer,a gas diffusion layer and a catalyst layer.It could maintain a high CO2 conversion Faraday efficiency in the presence of O2 in the CO2 reduction feed gas.The aniline was selected as an organic small molecule additive to prepare a composite polymer membrane(PIM-1/aniline)with high CO2 and O2 separation effect.The gas diffusion electrode of CoPc/CNT or Sn-based catalyst was equipped with this composite membrane to achieve O2-tolerance in electrochemical CO2 reduction.The design of such a hybrid electrode can reduce the purity requirement of the CO2 feed gas in CO2 reduction process.This provides a possibility for electrocatalytic CO2 reduction directly using air or industrial waste gas as raw feed gas in the subsequent practical commercial application.