Ni²⁺/Co²⁺ Induced Heterogeneous M_xP Electrocatalysts For Efficient Overall Water Splitting

As renewable energy,hydrogen has become the best alternative to fossil fuels because of its high energy density,zero emissions,and abundant raw materials.In various hydrogen-producing routes,electrochemical water splitting not only can realize a green conversion from electric energy into chemical energy but also offers a promising platform for utilizing intermittently renewable energy sources(e.g.,wind and solar energies).To improve the efficiency of water splitting,precious Pt-based and Ir/Ru-based electrocatalysts are usually employed in the practical electrolysis to reduce the activation energy barriers of two core half-reactions involved in water splitting,i.e.,hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),respectively Unfortunately,the large-scale utilization of these noble metals has been severely limited to their scarce reserves and high cost.Transition metals have similar d-orbital electronic structures as noble metals and are abundant,which makes non-noble transition metalbased compounds(eg.,sulfides,nitrides,phosphides,and carbides)become the potential electrocatalysts to replace noble metal-based catalystsTransition metal phosphides(MxP)have an anisotropic triangular prism structure,which leads to more unsaturated surface atoms and higher intrinsic catalytic activity However,CoP catalysts still have some disadvantages,such as poor conductivity and low exposure density of active sites.To fabricate COxP catalysts with competitive catalytic performance to noble metals,the nanostructure and electronic structure modulation of CoxP will be researched to improve the conductivity and exposing the active sitesThe main research contents and achievements of this article include1.Aiming to address the issue of insufficient exposure of active sites and limited mass transfer kinetics of CoxP,the hierarchical nanostructures are introduced into the catalysts from the epitaxial growth ZIFs(Zeolitic Imidazolate Frameworks)precursors to fabricate carbon-based COxP.The nanorods’ structure is beneficial to improve the exposure density of active sites and the mass transfer efficiency.In addition,N-doped carbon can increase the conductivity and activity of carbon materials.This work provides a new idea for the design and synthesis of hierarchical nanostructures of metalorganic framework derivatives2.We fabricated a novel hybrid nanostructure with nitrogen-doped carbon(NC)supported transition metal phosphide nanorods though a Co(Ni)ion exchangephosphidation strategy derived from Zn/Co-ZIFs.The Co2P/CoP-NC-0.1(m(Co2+):m(Zn/Co-ZIFs)=1:10)catalyst prepared by the appropriate amount of Co2+induction shows excellent electrocatalytic performance.When the Co2P/CoP-NC-0.1 is employed as both the anode and cathode for overall water splitting,a potential as low as 1.61 V is needed to achieve the current density of 10 mA/cm2,and it still exhibits superior activity after continuously working for 30 h with nearly negligible decay in potential.3.The electrocatalytic activity of Co2P/CoP-NC induced by Co2+is better than that of NiP/Co2P/CoP-NC induced by Ni2+.The Co2P/CoP-NC catalyst with good threedimensional structure has larger specific surface area,electrochemical activity area,and lower interfacial charge transfer resistanceIn this thesis,a novel transition metal phosphide(TMP)/carbon electrocatalyst with high efficiency and stability was synthesized by constructing interface engineering and controlling nanostructures.The introduction of metal ions into the ZIFs precursor leaded to the change of microstructure and composition,so we explored the effects of nanostructures and heterostructures on the catalytic activity.The current work provided a new insight into the design and synthesis of highly active,stable,and novel structured TMP/carbon catalysts for electrocatalysis applications.