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Surface Reconstruction Of Nickel-based Electrocatalysts For Overall Water Splitting

Posted on:2023-09-06Degree:MasterType:Thesis
Country:ChinaCandidate:Z N HuangFull Text:PDF
GTID:2531307046491544Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
The production of high-purity hydrogen utilizing electrochemical water splitting technology is considered as one of the most promising approaches to solve the energy crisis and environmental problems.However,the sluggish kinetics of hydrogen and oxygen evolution reactions(HER and OER)hinders the actual water splitting efficiency.Nickel-based electrocatalysts have been under the spotlight as promising substitutes of high-cost noble-metal materials for water splitting in alkaline media,but suffer from high activation overpotentials.Meanwhile,it has been well established that the surface reconstruction would take place on nickel-based compounds and their intrinsic activity originates from the reconstructed oxides/hydroxides/(oxy)hydroxides during the alkaline electrocatalytic process.Therefore,deeply understanding the surface reconstruction of nickel-based electrocatalysts and its influence on intrinsic electrocatalytic performance is significant to exploit effective electrocatalysts for water splitting.Here,nickel-based materials with surface engineering and early-transition-metal atomistic doping are used as the typical representatives.A synergetic combined experimental characterizations and theoretical calculations provide insights into the relationship among electronic structure,in-situ surface reconstruction and enhanced catalytic activity.The main content is as follows:(1)Ni X(X=O,S and P)interfaced with Ce O2 are prepared to investigate surface reconfiguration during the OER.As unveiled by in-situ Raman spectroscopy,Ce O2heterophases promote surface reconfiguration of Ni X,facilitating the formation of activated(oxy)hydroxide phase and the formed Ni OOH possess more oxygen defect sites when O is substituted by P or S.Density functional theory(DFT)calculations demonstrated that the introduction of Ce O2 and oxygen vacancy can regulate the interaction between the catalyst surface and oxygen-containing intermediates towards OER,contributing to highly enhanced OER activity.Ce O2-Ni3S2/NF and Ce O2-Ni2P/NF showed obviously improved TOF values as compared with Ce O2-Ni O/NF.Meanwhile,Ce O2-Ni3S2/NF exhibits a low overpotential of 255 m V to reach current density of 10 m A cm-2 in 1 M KOH,superior to most recently reported Ni-based electrocatalysts.(2)As the dopant,chromium(Cr)was introduced into Ni3N electrocatalysts to investigate the prominent role in improving activities for both HER and OER.The electrochemical and spectroscopic techniques unveil that Cr atoms not only modulates the electronic structure but also act as oxophilic sites for boosting the adsorption of oxygen-containing reaction species,thus leading to accelerate the self-reconstruction process for Ni3N.The in-situ generated Ni(OH)2 during HER would promote the dissociation of water,thereby accelerating the Volmer steps.Meanwhile,Cr-Ni3N/NF is eventually converted to Cr-doping Ni OOH serving as the actual active sites in the OER process.As a result,the Cr-Ni3N/NF can deliver a current density of 10 m A cm-2 at a low overpotential of 72 m V and 243 m V for HER and OER in 1 M KOH,respectively.Moreover,when assembled as bifunctional electrodes for overall water splitting,it requires a cell voltage of 1.51 V to reach 10 m A cm-2 with remarkable long-term durability for 100 h at overpotential of 300 m V.In summary,we proposed feasible strategies to optimize the structure of nickel-based electrocatalysts to promotes surface reconstruction and enhance the catalytic performance.This work will provide a guideline for the rational design of highly efficient electrocatalysts for water splitting from the viewpoint of structure-property relationships.
Keywords/Search Tags:Nickel-based electrocatalysts, doping, heterointerfaces, in-situ reconstruction, HER, OER
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