Controllable Construction Of Three-Dimensional Transition-Metal Dichalcogenide Nanoarray Electrodes For Enhanced Hydrogen Evolution Reaction

The rapid development of global economy has brought about the global huge energy demand and environmental concerns.In order to promote the sustainable development,numerous countries around the world are committed to seeking clean and renewable energy sources.Hydrogen as an environmentally friendly energy with zero-carbon emission and high energy density is expected to become an alternative to fossil energy in the future.Water electrolysis is one of promising highly efficient technologies to produce clean hydrogen at a large scale.Platinum group materials,are still recognized as the state-of-the-art electrocatalysts for hydrogen evolution reaction(HER),although their high cost and low elemental abundance limit their practical application in industry.It is necessary to develop low-cost and efficient non-noble metal electrocatalysts to meet the demand of hydrogen economy.A variety of non-noble metal HER electrocatalysts have been investigated,including transition metal alloys,phosphide,carbides,and sulfides,etc.However,the activity and stability of these materials still need further improvement compared with precious metals.This dissertation focuses on the development of nanostructured non-precious transition metal dichalcogenides HER electrocatalysts with the emphasis on improving electrocatalytic performances through enhancing the intrinsic activity of active site and increasing the quantity of accessible active sites.(1)Phase-Controlled Synthesis of NiSe/1T-MoSe2 Heterostructured Nanowire Arrays for Enhanced Hydrogen EvolutionPhase-engineered synthesis is challenging for constructing metallic-phase 1T-MoX2 for better electrocatalysis than their semiconducting counterparts.We synthesized NiSe nanowire arrays with controllable morphology on the surface of nickel foam substrate,followed by the secondary growth of MoSe2 nanosheets to construct the NiSe/1T-MoSe2 heterogeneous nanostructures.Such the structure of three-dimensional(3D)NiSe/1T-MoSei not only increases the activity areas,but also stabilize the metastable and highly active 1T phase MoSe2.Based on Raman,XPS spectra and atomic-resolution HAADF-STEM results,it is found that NiSe nanowire cores enable the growth of stable 1T-phase MoSe2 through the effective electron injection from NiSe,achieving the core/shell heterostructures of 1T-MoSe2 nanosheets aligning on NiSe nanowire arrays.Benefiting from the electron injection from NiSe to MoSe2,the increase of d-orbital electron density of transition metal causes destabilization of pristine 2H phase MoSei and favors its phase transition to metallic IT phase.Moreover,NiSe can facilitate the water dissociation step while lT-MoSe:is highly active for hydrogen formation step.Combining these two components together synergistically promotes the two elementary steps in alkaline HER.As a result,the developed NiSe/1T-MoSe2heterostructured nanowire arrays exhibit superior electrochemical HER activity in terms of a low overpotential of 200 mV to reach a current density of 50 mA cm-2 in 1.0 M KOH,outperforming other MoSe2 based catalysts.Besides,it delivers remarkable long-term stability for HER.Such catalytic activity and stability suggest that the current strategy may provide a new approach for the design and preparation of 1T-MoX2-based heterostructures with superior catalytic performance for diverse applications.(2)Fe/P Dual Doping Boosts the Activity and Durability of CoS2 Nanowires for Hydrogen EvolutionCoS2 is regarded as alternative electrocatalyst for HER while the activity and durability still cannot meet the criteria for applications.Here,we develop a strategy to simultaneously boost the HER activity and durability of CoS2 by fabricating polycrystalline nanowire(PCNW)arrays with dual doping of Fe and P.The 3D hierarchical Fe/P-CoS2 PCNW nanowires was constructed on carbon cloth(Fe/P-CoS2/CC)electrode.In brief,Fe doped Co3O4/CC precursor was grown on carbon cloth through solvothermal reaction followed by annealing in air.Fe-CoS2/CC was then obtained by the sulfurization of Fe-CO3O4/CC precursor.Fe/P-codoped CoS2 electrode was prepared by an additional phosphidation process.The results demonstrated that Fe or P doping didn't affect the structure of cubic CoS2 while Fe-doping increased the HER active sites and facilitated the charge transfer and P-doping accelerated the reaction kinetics,greatly boosting the intrinsic HER activity.Moreover P-doping obliterated the anti-bonding eg*orbitals to enhance the chemical bonding between Co and ligands,enhancing the chemical stability of CoS2.Consequently,such Fe/P-CoS2 nanowire arrays exhibit excellent HER activity with a low overpotential of 78 mV at 10 mA cm-2 and a small Tafel slope of 56 mV dec-1 as well as robust stability for HER.It is believed that these results may inspire the design and fabrication the HER electrocatalysts with enhanced activity and durability by dual doping with different components.