Morphology And Electronic Structure Tuning Strategies To Construct Transition Metal-based Electrocatalysts For Efficient Water Electrolysis

Faced with the exhaustion of non-renewable resources and the need for green environmental protection,it is a new challenge to find new environmentally friendly and renewable clean energy.Among them,the hydrogen produced by the water electrolysis for hydrogen production technology is not only green and environmentally,but also renewable.The water electrolysis reaction consists of two half-reactions,namely hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Due to the kinetics sluggish made the large overpotential,thus leading to a low hydrogen production efficiency.Therefore,it is urgent to search efficient and inexpensive electrocatalysts to reduce the overpotential of HER and OER reactions.At present,noble-metal Pt,Ir,and Ru-based catalysts exhibit the best performance,but the scarcity of precious metals seriously hindered their extensive development and application.Therefore,it is of great significance to develop and synthesize non-precious metal-based electrocatalysts with high performance,durability,and inexpensive.It is worth noting that there are fewer catalysts with both highly efficient HER and OER properties in the same electrolyte.Therefore,the research and design of bifunctional non-noble metal based electrocatalyst is beneficial to simplify the system and reduce the production cost.Based on the above analysis,the synergistic effect between effective regulation strategies is beneficial to improve the catalytic activity,stability,and durability of electrocatalysts.Therefore,the main contents of this thesis are as follows:（1）Electrospun Prussian blue analogue derived Ni Co alloy nanoparticles encapsulated in nitrogen-doped carbon nanofibers（Ni Co@NC）are adopted for neutral overall water splitting.The optimal Ni Co@NC-900 electrocatalyst exhibits the best electrocatalytic activity toward HER and OER in 1 M phosphate-buffered saline（PBS,p H 7）,respectively.More importantly,a neutral electrolyzer using Ni Co@NC-900 as both HER and OER electrodes achieves high stability with over 140 h and requires a low cell voltage of 1.75 V at 10 m A cm^-2.The remarkable stability and superior activity origin from the unique hierarchically porous and encapsulated structure,large surface area,abundant exposing active sites,and synergistic effect between the highly catalytic active Ni Co alloy nanoparticles and high-conductivity N-doped carbon nanofibers.This work can provide a new way to develop non-precious catalysts for highly stable water splitting in neutral media or seawater.（2）An in-situ integration engineering strategy of oxygen-vacancy and core–shell heterojunction to fabricate an anemone-like Co P@Co OOH core-shell heterojunction with rich oxygen vacancies supported on carbon paper（Co P@Co OOH/CP）,is described.Benefiting from the synergy of Co P core and oxygen-vacancy-rich Co OOH shell,the as-obtained Co P@Co OOH/CP catalyst displays low overpotentials at 10 m A cm^-2 for HER（89.6 m V/81.7m V）and OER（318 m V/200 m V）in neutral and alkaline media,respectively.Notably,a two-electrode electrolyzer,using Co P@Co OOH/CP as bifunctional catalyst to achieve 10 m A cm^-2,only needs low-cell voltages in neutral（1.65 V）and alkaline（1.52 V）electrolyte.Besides,systematically experimental and theoretical results reveal that the core-shell heterojunction efficiently accelerates the catalytic kinetics and strengthens the structural stability,while rich oxygen-vacancies efficiently decrease the kinetic barrier and activation energy,and reduce the energy barrier of the rate-determining-step for OER intermediates,thus intrinsically boosting OER performance.This work clearly demonstrates that oxygen-vacancy and core-shell heterojunction engineering provide an effective strategy to design highly-efcient non-precious,bi-functional electrocatalysts for p H-universal water splitting.（3）A cation-doping and oxygen-vacancy engineering strategy to fabricate Ru/Rh-doped Fe OOH nanoarrays with abundant oxygen-vacancies in-situ grown on Ti₃C₂T_x MXene（Ru/Rh-Fe OOH@Ti₃C₂T_x）as highly-efficient OER electrocatalysts,is proposed.Benefiting from Ru/Rh-cation regulation,oxygen-vacancy engineering,and heterojunction synergy between Ti₃C₂T_x MXene and modulated Fe OOH,the optimized Rh/Ru-Fe OOH@Ti₃C₂T_xMXene electrocatalysts exhibit excellent OER activities and remarkable stabilities with 100 h.Particularly,3%Rh-Fe OOH@Ti₃C₂T_x MXene electrocatalyst only needs a 223 m V overpotential at 10 m A cm^-2 and 306 m V to reach 100 m A cm^-2,which is superior to commercial Ir O₂ catalyst and most reported oxyhydroxide-based electrocatalysts.Further,systematically theoretical caculation,kinetics,thermodynamics,and microstructural analysis verify that the integration of Ru/Rh-cation doping and oxygen vacancy can obviously enhance the intrinsical conductivity and lattice defects of Fe OOH and expose more active sites,thereby decreasing the adsorption/desorption energy barrier and activation energy,and improving the specific activity and catalytic kinetics of electrocatalysts,whereas in-situ hybridization with MXene can strengthen the structural stability.This work clearly confirm that cation-doping and oxygen-vacancy engineering offers a joint strategy for the electronic structure modulation and design of highly-efficient inexpensive OER electrocatalysts.