Research On Nickel-based Electrocatalysts For Water Splitting

In current society,developing clean energy is becoming more and more important with increasing utilization of traditional fossil fuels and environmental pollution.As a high density and pollution-free energy,hydrogen has triggered great attention in academic and industrial fields.In this regard,water electrolysis provides an efficient method to generate hydrogen.Unfortunately,lack of highly efficient,stable and cheap catalyst limits its farther development,especially for hydrogen evolution and oxygen evolution reactions.So,how to design and synthesize non-precious metal catalysts with outstanding performance is critical scientific issue with great researchful and practical values.On account of the above problems,the dissertation focuses on the rational design and simple synthesis route of catalysts based on nickel for hydrogen and oxygen evolution with outstanding performance in alkaline media.At the same time,combing with X-ray adsorption spectra,transmission electron microscope and other characterization instruments,the functions of interfaces and amorphization for catalytic performance are also discussed in detail.The main contents of the dissertation are as follows:The hydrogen evolution performance of nickel phosphides was improved through interfacing engineering.Specifically,the interfaces between Ni2P and Ni12P5 were constructed by one-step calcination in inert atmosphere with introduction of amount of water.In 1 M KOH solution,the anundant interfaces endow the catalyst(denoted as Ni2P-Ni12P5/NF)with excellent electrocatalytic hydrogen evolution reaction(HER)activity(?@10 mA/cm2=76 mV).Meanwhile,the Ni2P-Ni12P5/NF exhibits much lower overpotential at high current density(>80 mA/cm2)and better long-term stability compared with Pt/C/NF.The theoretical calculation shows the altered electronic states at interfaces optimize hydrogen adsorption and thus enhance the hydrogen evolution performance.In addition,outstanding overall water splitting performance is also obtained on combinations of the NiFe-LDH(anode)and Ni2P-Ni12P5/NF(cathode).The work offers simple and facile route of constructing abundant interfaces between transition metal phosphide electrocatalysts for hydrogen evolution reaction.The amorphous catalyst(denoted as NiFe/C)with brilliant alkaline oxygen evolution performance was first prepared by a simple route.Through the facile freezedry method,the nanoclusters can be obtained on porous carbon black.Additionally,the homologous crystalline catalyst(denoted as C-NiFe/C)exhibits inferior catalytic performance(?@10 mA/cm2=370.39 mV)to amorphous counterpart(?@10 mA/cm2=269.55 mV)in 1 M KOH solution.The X-ray adsorption spectra and images of highresolution transmission electron microscope confirmed the nanoclusters are consisting of nickel-iron oxyhydrate,which play an essential role in catalytic process.Moreover,the mass activity and TOF of NiFe/C are 336.5 A/g and 8.14 s-1 when the overpotential is 300 mV,respectively,in 1 M KOH electrolyte.The work opens a novel avenue for the development of amorphous catalyst for oxygen evolution reaction.Based on NiFe/C,NiFeCu enhanced long-term stability through introducing copper into NiFe/C.Chronoamperometry measurement at 40 mA/cm2 reveals no decay over 48 hours.It is worthy noted that NiFeCu shows preferable intrinsic activity than NiFe/C,including mass activity and TOF.At 300 mV overpotential,the mass activity and TOF is 1061 A/g and 37 s-1,respectively.This project offers an innovative idea for improving intrinsic activity in next step.