Preparation Of Several Transition Metal Catatysts And Studies On Their Performance Toward Oxygen Evolution Reaction

This paper, based on transition metal catalyst（Ni, Co and Fe） for oxygen evolution reaction（OER）, constructed three kinds of OER anode materials, namely CoFe₂O₄-CNTs, NiS@N/S-C and Ni₃N@C. The main purpose is to reduce the overpotential for oxygen evolutionon, decrease the energy consumption, and improve energy conversion efficiency. CNTs and carbon material formed by the in-situ could be a carrier, increase the electrons transfer, and protect nanoparticles to enhance the dynamic for OER and improve the stability of the catalyst. Simultaneously, N and S heteroatoms modulate the electron-donating / withdrawing capability of carbon support, improving the conductivity of the catalyst, thereby enhancing the material electrocatalytic activity for OER. The morphology, structure and composition of these three kinds of anodic materials were characterized by means of characterization methods. The electrocatalytic performance of anodic materials also was detected with the three-electrode system in the electrochemical workstation. The main research contents are as follows:（1） The CoFe₂O₄ nanoparticles were loaded on the surface of CNTs through the hydrothermal method, forming the CoFe₂O₄-CNTs nanocomposite. The results show that the spinel CoFe₂O₄ nanoparticles are uniformly dispersed on the CNTs surface; In order to verify the role of CNTs, the content of CNTs characterized by TG is 40.2 %. The electrocatalytic activity and stability of CoFe₂O₄-CNTs nanocomposite were tested in 1 M KOH electrolyte.The experimental results show that CoFe₂O₄-CNTs nanocomposite exhibited good catalytic activity, as evidenced by small onset potential at 1.54 V. The introduction of CNTs can improve the current density and the catalytic activity of hybrids. The activity did not change obviously after the stability test at a constant current density of 10 mA cm-2 for 11 h.（2） The NiS@N/S-C nanocomposite structure was obtained by high temperature pyrolysis of as prepared Ni based complex with S and N atoms under a NH3 atmosphere. The results showed that the NiS nanoparticles were dispersed evenly on the carbon substrate formed by the in-situ; At the same time, the N、S co-doped carbon substrate played an important role to promote the OER activity through structure and electronic modification of the carbon. The activity and stability of Ni S@N/S-C nanocomposite were tested in 1 M KOH electrolyte. The experimental results showed that NiS@N/S-C nanocomposite depicted high electrocatalytic activity with small onset potential at 1.56 V. There is no activity loss after the stability test at a constant current density of 10 mA cm-2 for 10 h.（3） The Ni₃N@C nanocomposites were prepared by one-step pyrolysis method. The results show that the uniformly dispersed Ni₃ N nanoparticles with a diameter of 200 nm were coated with a thin layer of carbon layer; The carbon layer formed by the in-situ was uniformly distributed by mapping characterization; The coated carbon layer can conduct electrons, and play a role in protecting the Ni₃ N and improving the stability of the catalyst. The activity and stability of Ni₃N@C nanocomposite were performed in 1 M KOH electrolyte. The experimental results indicated that Ni₃N@C nanocomposite depicted high catalytic activity with small onset potential at 1.53 V and large current density. The activity can keep good after the stability test at a constant current density of 10 mA cm-2 for 10 h.