Preparation Of Heteroatom Modified Non-noble Metal Catalysts For Electrochemical Water And Seawater Splitting

Hydrogen has been considered to be one of the most promising candidates to address energy crisis and environment issues due to its high-energy density and environmentally benign.Electrochemical water and seawater splitting powered by renewable electricity sources is a promising technology to product“green hydrogen”,with the advantages of high purity products,simple process,and high conversion efficiency.Although noble metal-based materials are currently the benchmarks of highly efficient catalysts for water and seawater splitting,the rarity and high cost hinder their large-scale application.Furthermore,direct seawater splitting technology faces great challenges,including the chlorine evolution reaction that competes with oxygen evolution reaction（OER）,the corrosion of catalysts by abundant Cl^-ions in seawater,and the deposition of insoluble precipitates and microorganisms,thus leading to more demanding requirement for electrocatalysts.Although great progress has been made in the development of non-noble metal-based materials,most catalysts still exhibit high overpotentials and poor stability,which cannot meet the requirements of the actual industrial.Therefore,there is urgent to develop low-cost,highly efficient and stable non-noble metal catalysts to improve the efficiency and reduce the cost of water and seawater splitting,so as to promote their large-scale application.To overcome these difficulties encountered in electrodes for water and seawater splitting,a series of highly efficient electrocatalysts have been successfully developed based on heteroatom modification.Additionally,the roles of heteroatoms on the catalytic performance for water and seawater splitting were also explored.The main research contents included the following aspects.（1）N-doped Ni-Mo based sulfides for high-efficiency and stable hydrogen evolution reactionIn this work,N-doped Ni-Mo based sulfide（N-NiMo S）cuboid arrays was fabricated for highly efficient HER in alkaline solution.Systematic insights reveal that the incorporation of nitrogen not only modifies the electronic structures and d-band center of NiMo S,but also lowers the work function of NiMo S for facilitating electron transport,which increases the HER activity.Therefore,the N-NiMo S electrode exhibits outstanding HER activity,which requires the overpotentials of 68,250,and 322 m V at current densities of 10,500,and 1000 m A cm^-2,respectively,much superior than pure NiMo S and commercial Pt/C electrode.More impressively,the N-NiMo S catalyst can operated stably for 1000hours,demonstrating its outstanding durability for HER.This work presents an effective strategy to improve the activity and stability of bimetallic sulfides,which develops an idea for designing efficient catalysts.（2）Fe induced nanostructure reorganization and electronic structure regulation for accelerating oxygen evolution reactionIn this work,a self-template strategy with Fe³⁺etching was developed to fabricate Fe-Co Ni-OH nanosheet-assembled nanorod arrays,where smooth Co Ni-OH nanorod structure was used as a template.This three-dimensional hierarchical nanostructure fully exposes catalytic active sites for facilitating mass transfer.Additionally,the incorporation of Fe atoms efficiently enhances electronic conductivity of the Co Ni-OH electrode for rapid electron transfer,which improves the OER performance.Therefore,the Fe-Co Ni-OH electrode possesses highly efficient OER activity,which only requires extremely low overpotentials（210,248,304,and 349 m V）for driving the corresponding current densities(10,100,500,and 1000 m A cm^-2),much better than these of the Co Ni-OH and commercial Ru O₂.This work provides an effective self-template strategy to fabricate highly efficient and stable three-dimensional hierarchical catalysts for water electrolysis technology,which simultaneously increased the number and intrinsic activity of active sites.（3）In situ S leaching induces the formation of highly active Ni⁴⁺for water and seawater splitting at large current densitiesIn this work,a unique two-step oxidation method was developed for in-situ growth of Fe-NiSOH nanosheet arrays on nickel foam.The nickel foam substrate provided nickel sources for direct growth of the active materials to ensure a tight connection,which guarantees excellent electron transport and seawater corrosion resistance,so that it can stably operate in alkaline water and seawater.Systematic insights reveal that in situ S leaching not only promotes the self-reconstruction process,but also reduces the formation energy of Ni⁴⁺,thus triggering highly active lattice oxygen mechanism for OER cycle.Therefore,the Fe-NiSOH electrode possesses highly efficient OER performance in alkaline water and seawater,which can operate stably for long periods of time at the high current density of 500 m A cm^-2.This study provides an effective strategy for the construction of rapidly self-reconstructing catalysts to generate high valence metal species,and greatly promotes the development of alkaline water and seawater splitting.（4）Fe and Mo co-modified Ni₃S₂ nanosheet arrays for large-current-density seawater splittingIn this work,Ni₃S₂ nanosheet arrays with Fe and Mo co-modification（Fe Mo-Ni₃S₂）was fabricated as an efficient large-current-density seawater oxidation electrode.Systematic insights reveal that Fe and Mo co-modification not only effectively regulates the electronic structure of the Ni₃S₂ catalyst for improving electron transport process,but also promotes the formation of more stable Fe Mo-NiOOH species on the surface of the Fe Mo-Ni₃S₂ catalyst surface as the active sites,thus essentially improving the OER activity and seawater corrosion resistance.Therefore,the Fe Mo-Ni₃S₂ electrode possesses excellent performance for large-current-density seawater oxidation,which only requires the low overpotentials of 242 and 275 m V to drive the current density of 100 and 500 m A cm^-2 in extremely harsh 6 M KOH seawater.Impressively,the Fe Mo-Ni₃S₂ electrode can operate stably at the large current density of 500 m A cm^-2 over 500 hours.This study not only presents a highly efficient and stable catalyst for large-current-density seawater splitting,but also provides an important idea for studying the structure-activity relationship of muti-heteroatom co-modified catalysts.