Investigation On Transition Metal Catalysts For Electrocatalytic Water Splitting

Hydrogen（H₂）has been identified as the most potential energy carrier alternative to fossil fuels owing to its environmentally favorable,many forms of utilization and high gravimetric energy density.The electrocatalytic water splitting is an ideal way to produce hydrogen in a variety of hydrogen production processes.The kinetics of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）are slow and require higher overpotential to drive the reaction,resulting in low energy conversion efficiency.The development of efficient and stable catalysts is one of the ways to solve the above problems.In this dissertation,a series of catalysts were prepared by doping with transition metal oxides for oxygen evolution reaction and by constructing interface with transition metal phosphide for hydrogen evolution reaction.The main research contents are as follows:（1）The Ru doped Co₃O₄ catalyst（Ru-Co₃O₄）was synthesized on carbon paper by a thermal decomposition method for oxygen evolution reaction of acidic and alkaline conditions.The effect of Ru doped catalyst on OER was investigated,and the results showed that Ru doped catalyst showed excellent activity and stability.In detail,at a current density of 20 m A cm^-2,it requires only 225 m V of overpotential,and can run steadily for 600 h in 0.5 mol L^-1 H₂SO₄.It requires only 223 m V of overpotential,and can run steadily for 230 h in 1.0 mol L^-1 KOH.The excellent OER performance was attributed to the accelerated reaction kinetics and charge transfer ability,exposure of more active sites after Ru doping.（2）In order to obtain a stable OER catalyst with high current density,the Ru-doped Mn Co₂O_4.5 catalyst(5%-Mn Co₂O_4.5)was synthesized on carbon paper by thermal decomposition method.The influence of Ru-doped OER was explored.The results show that 5%Ru-Mn Co₂O_4.5 catalyst exhibits excellent OER activity and stability at high current density.In 0.5 mol L^-1 H₂SO₄,only 277 m V of overpotential is required at a current density of 100 m A cm^-2,and the stable operation can be 290 h.In 1.0 mol L^-1 KOH,only 282 m V of overpotential is required at a current density of100 m A cm^-2 and stable operation can be achieved for 300 h.The excellent OER activity is attributed to Ru doping which provides abundant active sites,reduces activation energy of reaction and promotes mass transfer process.（3）In order to obtain the cathode catalyst for electrocatalytic water splitting,the crystalline/amorphous In₃Ni₂/Ni P_x composite electrocatalyst was constructed on carbon paper by one-step electrodeposition method for alkaline HER.The results show that the In₃Ni₂/Ni P_x catalyst exhibits excellent activity and stability in 1.0 mol L^-1 KOH.The results showed that In₃Ni₂/Ni P_x catalyst exhibited excellent activity with 55 m V overpotential at a current density of 10 m A cm^-2 and 112 m V overpotential at a current density of 100 m A cm^-2,which is better than amorphous Ni P_x catalyst and crystalline In₃Ni₂/Ni catalyst.Meanwhile,the catalyst has excellent stability and stable operation at a current density of 10 m A cm^-2 for 210 h.The outstanding HER activity of crystalline/amorphous In₃Ni₂/Ni P_x composite electrocatalysts is attributed to the exposure of more active sites,the excellent conductivity and electron transport properties,and the synergistic effect between the crystal In₃Ni₂ and amorphous Ni P_x.（4）The two-electrode of water splitting system uses In₃Ni₂/Ni P_x catalyst as the cathode and a 5%Ru-Mn Co₂O_4.5 catalyst as the anode.In 1.0 mol L^-1 KOH,the electrolyzer delivers a current density of 1.46 V at a current density of 20 m A cm^-2and 1.64 V at a current density of 100 m A cm^-2.The catalyst can be maintained 145 h at a current density of 20 m A cm^-2.In 0.5 mol L^-1 H₂SO₄,the electrolyzer delivers a current density of 1.64 V at a current density of 20 m A cm^-2 and 1.71 V at a current density of 100 m A cm^-2.The catalyst can be maintained for 165 h at a current density of 20 m A cm^-2.The study shows that the system possesses potential applications.