Reaction Center Design Of Supported Single-atom Electrocatalysts For Oxygen Reduction/Evolution Reaction

The development of non-noble metal catalysts for oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）is of great significance in energy conversion and storage technologies.M-N-C catalysts have unique electronic structure and active centers,making them one of the most promising electrocatalysts.In this dissertation,density functional theory was used to investigate the effect of the coordination environment on the electrocatalytic activity in Cu single-atom catalysts and Fe-based bimetal catalysts.The main conclusion are as follows:（1）The effect of introducing hetro-atoms such as B,N,P and S into the first and second coordination spheres of the Cu N₄active center on the catalytic activity of ORR was investigated.It is shown that the catalysts with Cu N₃and Cu N₄S₂（II）reaction center exhibited better ORR catalytic activity than commercial Pt(η^ORR=0.45 V)with overpotentials of 0.32 V,0.37 V and 0.49 V.respectively.The orgin is ascribed to the special coordination configuration which increases the charge of the active center and tunes the fine structure of the d-band,optimizing the intermediate binding strength.In addition,based on the coordination configuration of the good catalysts,other transition metals（Mn,Fe,Co,Ni and Zn）were applied as active centers,and Co N₄B₂（II）(η^ORR=0.24 V),Co N₄S₂（II）(η^ORR=0.39 V),Ni N₄P（II）(η^ORR=0.43 V)and Ni N₄S₂（II）(η^ORR=0.45 V)exhibit good ORR catalytic activities.These findings point out the importance of the coordination environment and provide a new direction for the synthesis of efficient electrocatalyst materials.（2）A series of N-doped graphene with Fe-M bimetal sites（Fe TMN₆）were constructed,where TMs are transition metals such as Cr,Mn,Co,Ni,Cu,Zn,Mo,Ru,Rh,W,Re,and Os elements.Among them,catalysts with Fe Co N₆（I）,Fe Zn N₆（I）,Fe Ru N₆（I）,Fe Rh N₆（I）and Fe Ir N₆（I）reaction centers perform excellent ORR catalytic activities with overpotentials of 0.34 V,0.41 V,0.42 V,0.30 V and 0.26V,respectively.The catalysts with Fe Rh N₆（I）and Fe Ir N₆（I）exhibited better OER catalytic activity than commercial Pt O₂with overpotentials of 0.45 V and 0.31 V,respectively.In other words,Fe Rh N₆（I）and Fe Ir N₆（I）exhibit excellent bifunctional catalytic activities.Surface protonation simulations of Fe/Ru-N-C[Fe Ru N₆（I）],Fe/Rh-N-C[Fe Rh N₆（I）],Fe/Os-N-C[Fe Os N₆（I）]and Fe/Ir-N-C[Fe Ir N₆（I）]were carried out to explore the structure stability in acidic environment,and it was found that the structure and ORR catalytic activity of Fe/Os-N-C[Fe Os N₆（I）]was remained.Meanwhile,it was confirmed that Fe/Ru-N-C[Fe Ru N₆（I）],Fe/Rh-N-C[Fe Rh N₆（I）],Fe/Os-N-C[Fe Os N₆（I）]and Fe/Ir-N-C[Fe Ir N₆（I）]also exhibit good thermal stability.