Fabrication And Electrocatalytic Water Splitting For Hydrogen Evolution Study Of Ni-based Electrocatalysts

The depletion of the unsustainable fossil fuels drives the exploration of renewable and clean energy.Hydrogen,as a high energy density,abundant reserves,sustainable and zero emission of greenhouse gas,is now considered as the primary choice.Among the various hydrogen production methods,electrocatalytic water splitting can easily and widely produce high-purity hydrogen,but it requires a high-efficient and durable electrocatalyst to keep high and stable current density at low overpotential.Although rare metals?e.g.,Pt,Ir and Ru?based electrocatalysts possess excellent hydrogen evolution reaction?HER?performance,the high cost and scarcity of noble metals are seriously detrimental to the large-scale commercial application of clean energy technology.Recently,with the assistance of the non-noble metal based compounds,electrocatalytic hydrogen evolution has aroused tremendous attention.In particular,earth abundant materials,such as transition metal phosphides,carbides,nitrides,demonstrate highly active and efficient activity toward HER under different conditions.In the past time,Ni-based electrocatalysts have been reported as outstanding catalysts.Therefore,this doctoral dissertation focuses on the fabrication of Ni-based electrocatalysts and the study of their electrochemical performance.The main contents in this thesis are as follows:?1?Self-supported Mn-doped NiSe₂ nanosheets anchored on carbon paper was successfully fabricated by phase-controlled selenizing reaction,as a higher efficient and stable three dimensional HER electrocatalyst,possess high electrocatalytic performance than pure NiSe₂ NSs/CP.Our results demonstrated that Mn-doped NiSe₂ NSs electrode demanded overpotentials of 87 mV vs.RHE at 10 in 0.5 M H₂SO₄.The effects caused by Mn doping for HER performance were also investigated by DFT.DFT calculations provided that Mn doping can weaken the interaction between surface and H atoms,which results that Mn-doped NiSe₂ possesses lower thermo-neutral hydrogen adsorption free energy.?2?Self-supported 3D Mn-doped NiP₂ nanosheets on carbon cloth?Mn-NiP₂NWs/CC?is prepared by phase-controlled phosphating reaction route by using vacuum encapsulation technique,and were evaluated over the wide range of pH 0–14 for HER.Our experiments demonstrated that only 69,97,and 107 mV of over-potentials are demanded for Mn-NiP₂ NSs/CC to achieve 10 mA cm^-2 in 0.5 M H₂SO₄,1.0 M KOH,and 1.0 M PBS,respectively.DFT calculations provided a strong proof that Mn doping can weaken the bonds between surface and H atoms,resulting in lower thermo-neutral hydrogen adsorption free energy.?3?Self-supported 3D iron nickel poly-phosphide nanosheets on carbon paper was successfully fabricated by one-step Fe-Ni NSs precursor phosphating and further probed the local coordinate and electronic structure by X-ray absorption near-edge structure spectroscopy Benefiting from the controllable composition,the optimized ternary Ni-Fe-P nanosheets electrode possessed excellent electrocatalytic performance and outstanding durability.Only 56 mV of overpotential in 0.5 M H₂SO₄ is required for optimized ternary Ni-Fe-P nanosheets to reach 10 mA cm^-2,which possesses much better electrocatalytic performance than pure NiP₂ under identical conditions.The XANES,XPS and DFT calculations indicate that the Ni-P bonds elongated and less electrons transferred from Ni to P,which enhance the metallicity of Ni to improve the HER performance of NiP₂ with the Fe ions incorporation into the system.The above analysis indicated that electronic structure engineering of the NiP₂ catalyst by the strategy of Fe-doping has triggered the synergistic effect to enhance the catalytic kinetics,resulting in improved electrocatalytic performance.?4?Self-supported 3D CoP₃@NiP₂ hierarchical architecture was synthesized by using the phase-controlled phosphating reaction route on CP.In this 3D self-supporting composite electrode,the crystalline Ni?OH?₂ nanosheets were grown on CP,and the high crystallinity Co?OH?F nanowire was grafted on the Ni?OH?₂ nanosheet by the hydrothermal reaction.The Co?OH?F@Ni?OH?₂ composite was further phosphating with red P element by a phosphorization approach.Our results demonstrated that CoP₃@NiP₂/CP electrode demanded overpotential of 57 mV vs.RHE at 10 in 0.5 M H₂SO₄.The unique 3D hierarchical architecture had a bigger surface for providing more active sites and accelerating the releasing of generated bubbles.In addition,the synergetic effect between CoP₃ nanowire and NiP₂ nanosheet also improved the supercapacitor performance.Our results demonstrated that CoP₃@NiP₂/CP electrode demanded overpotential of 57 mV vs.RHE at 10 in 0.5 M H₂SO₄.