Synthesis Of Ni-based Catalysts For Electrocatalytic Water Splitting

Electrocatalytic water splitting is a promising strategy for sustainable hydrogen generation and electric energy storage because of simple production process and high purity hydrogen product.However,the sluggish electrode reactions lead to high overpotentials,which can decrease energy conversion efficiency and hinder its large-scale commercial applications.For water splitting,using high-performance catalysts can efficiently reduce its overpotentials,which leads to improving energy conversion efficiency.Although noble Ru-,Ir-and Pt-based electrocatalysts have shown good activity for water splitting,their low abundance and high price hamper the practical applications.Hence,in this study,rational structure was constructed to optimize catalysts' active sites,stability,electrical conductivity and hydrophilic-aerophobic feature for excellent water-splitting performance.Besides,this study reveals some relations between catalysts' structure and composition and their water-splitting performance.In the study,four high-performance Ni-based catalysts for water splitting were rationally designed and prepared,and the main research results as follows:(1)Small Ni3Sn2@NiO,Hy nanoparticles with abundant surface defects derived from intermetallic Ni3Sn2 nanoparticles supported on carbon nanotubes(Ni3Sn2@NiOxHy/CNT)were prepared via an aqueous-phase reduction method and a subsequent in-situ surface selective removal by electrochemical oxidation.Compared with Ni nanoparticles without Sn,the Ni3Sn2@NiOxHy nanoparticles owns a large amount of surface defects,which can not only expose more active sites,but also enhance its intrinsic activity.Besides,the small size of nanoparticles and the electrical conductivity of CNT can also improve the catalyst's activity.Therefore,Ni3Sn2@NiOxHy/CNT requires only an overpotential of 250 mV to achieve 10 mA cm-2 for oxygen evolution reaction(OER).(2)Three-dimensional(3D)N-doped carbon nanotubes encapsulating Ni/MoN heterostructures directly grown on carbon cloth(Ni/MoN@NCNT/CC)was prepared through chemical vapor deposition.Constructing heterostructure by combining Ni and MoN can expose abundant active sites and enhance the intrinsic activity.In addition,the NCNT with high conductivity and good mechanical stability can provide effective electron transport and improve the catalyst's durability.Besides,3D structure of NCNT on carbon cloth is beneficial to exposing more active sites,accelerating gas bubbles release,and contacting the electrolyte.As a result,the Ni/MoN@NCNT/CC needs overpotentials of 252 and 207 mV and a cell voltage of 1.699 V to reach 10 mA cm-2 for OER,hydrogen evolution reaction(HER)and overall water splitting,respectively.Particularly,for HER,it can maintain a consistent potential at 100 mA cm-2 for 100 h.(3)Hierarchical CoNi2S4@NiMn-layered double hydroxide heterostructure nanoarrays on superhydrophilic carbon cloth(CoNi2S4@NiMn LDH/SCC)was prepared by a hydrothermal method.Constructing heterostructure by coupling CoNi2S4 with NiMn LDH not only owns a bifunctional feature for water splitting via integrating highly-active single component,but also enhance the intrinsic activity through interfacial effects.Moreover,the highly conductive CoNi2S4 cores serve as efficient electron-transfer channels to compensate the poor conductivity of NiMn LDH,while the NiMn LDH shells ensure the durability of the catalytic system by acting as a protective layer under anodic potential.Besides,the superhydrophilic feature of carbon cloth support is beneficial to the uniform growth of catalysts and contacting the electrolyte.Accordingly,the CoNi2S4@NiMn LDH/SCC needs overpotentials of 269 and 1 84 mV and a cell voltage of 1.691 V to reach 100 mA cm-2 for OER,HER and overall water splitting,respectively.Furthermore,for OER,its overpotential can remain constant at 100 mA cm-2 for 12 h.(4)3D heterostructured NiCoP@NiMn LDH arrays supported on Ni foam(NiCoP@NiMn LDH/NF)was prepared via a facile hydrothermal reaction and phosphorization.Constructing heterostructure by coupling NiCoP and NiMn LDH not only possesses the bifunctional feature for water splitting by combining the highly-active property of individual NiCoP and NiMn LDH,but improves the catalyst's intrinsic activity via the effective interface engineering.In addition,the NiCoP core material serves as fast electron transfer channels to enhance the electrode's electrical conductivity.Besides,3D arrays supported on Ni foam with network structure is beneficial to exposing more active sites,facilitating gas bubbles release,and touching the electrolyte.Consequently,the NiCoP@NiMn LDH/NF only needs overpotentials of 293 and 116 mV and a cell voltage of 1.642 V to achieve 100 mA cm-2 for OER,HER and overall water splitting,respectively.Besides,its cell voltage hardly changes at 100 mA cm-2 for 50 h.