Preparation Of New Transition Metal-based Nanomaterials & Their Performance In Electrocatalytic Water Splitting

Hydrogen becomes an ideal carrier for clean energy conversion and energy storage because of its high energy density,cleanness and reproducibility.Electrocatalytic water decomposition reactions consisting of hydrogen evolution reactions(HER)and oxygen evolution reactions(OER)are considered to be an efficient,pollution-free and recyclable source of hydrogen.Up to now,platinum-based(Pt)and iridium-based(Ir)are the best electrocatalytic catalysts for HER and OER respectively.But they are difficult to be applied in large-scale industrialization.Transition metal compounds such as Ni,Fe and Co are an ideal substitute for noble metal-based catalysts due to their abundant reserves,low cost and tunable electronic structure.Therefore,a series of new transition metal-based nanomaterials has been designed and prepared,and their electrocatalytic hydrogen and oxygen evolution properties were studied systematicly.As shown in the follows:1.The coupling of NiFeP and amorphous NiFeO_x supported on Ni foam was prepared with plasma assisted strategy and the electrocatalytic oxygen evolution performance was investigated in alkaline medium systematicly.It was found that the metal-like properties of NiFeP greatly reduce the charge transfer resistance and facilitate the rapid transfer of electrons.Amorphous NiFeO_x has more lattice distortion and produces larger electrochemical active surface area.The resultant NiFeO_x/NiFeP showed excellent electrocatalytic oxygen evolution performance.In the alkaline solution,the overpotential was only 165 m V at the current density of 10mA cm^-2,and the Tafel slope was only 57.9 mV dec^-1,with good stability.Finally,based on DFT calculations,the reasons for the improvement of the electrocatalytic performance of NiFeO_x/NiFeP were revealed from the atomic level.2.A novel Ni₂P@CoP/FeOOH nanowire array supported on Ni foam was designed and synthesized as a cheap and efficient transition metal-based bifunctional catalyst.The nanorod arrays structure has a large specific surface area,which facilitates the full contact between catalyst and electrolyte and expedites the desorption of product gas.FeOOH can promote the adsorption and cleavage of water molecules while CoP can improve the electron transfer during electrocatalytic reaction,and the presence of Ni₂P considerably enriches the active sites of the catalyst.Ni₂P@CoP/FeOOH showed excellent HER and OER catalytic activity in alkaline solution as well as good stability.The overpotential was 110 mV and 195 mV for HER and OER to afford a current density of 10 mA cm^-2,and the Tafel slope was 72.2mV dec^-1 and 67.1 mV dec^-1,respectively.