Synthesis And Electrochemical Properties Of Non-Noble Metal Based Electrocatalysts

The excessive consumption of non-renewable energy and the sharp deterioration of environmental pollution problems force people to vigorously develop safe,clean and efficient renewable new energy.The electrocatalytic water splitting to produce hydrogen is the most effective way to develop renewable and clean energy about hydrogen.However,the best comprehensive performance of oxygen evolution reaction?OER?electrode catalysts in acidic and alkaline solutions are some rare and expensive noble metal oxides,such as RuO₂ and IrO₂,which seriously restrict the large-scale commercial application of electrocatalytic water splitting devices.Therefore,the development of earth-abundant-electrocatalysts for oxygen evolution reaction?OER?is one of the promising ways to achieve efficient water-splitting for hydrogen production.Transition metal?Ni,Co,Fe?compounds have attracted more and more attention from scholars due to their advantages of abundant reserves,reducing costs,high OER activity and stability.Aiming at the development of cheap and efficient non-noble metal based electrocatalysts,the layered NiFe bimetallic hydroxide?LDH?and mesoporous cobalt tetroxide?Co₃O₄?were obtained through simple preparation processes,and their OER electrocatalytic properties were studied.For the first part of this paper,Ni_1-xFe_xOOH?x=0-1?LDH catalysts with different atomic ratios were synthesized.OER electrochemical tests determine that the best performing catalyst is a catalyst with an atomic ratio of Ni/Fe=5 LDH.The obtained Ni/Fe=5 LDH catalyst has multi-slit channel layered structure,and has higher OER electrocatalytic activity than RuO₂ and IrO₂,with lower overpotential,turnover frequency?TOF?and Tafel slope than RuO₂ and IrO₂.In addition,the effects of pH and temperature on the OER electrocatalytic performance of Ni/Fe=5 LDH catalyst were analyzed and tested to study the reaction mechanism of OER and apparent electrochemical activation energy?E_a?of Ni/Fe=5 LDH catalyst.For the second part of this paper,the Co₃O_4-?catalyst with large number of vacancies on the mesoporous surface is also obtained by calcining the SBA-15 template.Morphological characterization showed that the Co₃O_4-?is a rod three-dimensional?3D?mesoporous structure.The Co₃O_4-?catalyst can show excellent OER electrocatalytic activity and stability in the alkaline environment,which is far better than commercial Co₃O₄.In addition,the Co₃O_4-xF_x catalyst with oxygen vacancy on surface and the F-doped mesoporous structure was obtained by the treatment with XeF₂.The Co₃O_4-xF_x catalyst has the same mesoporous 3D rod structure as the Co₃O_4-?catalyst and the optimal OER electrocatalytic activity was Co₃O_3.8F_0.2.2 catalyst.The doping of F greatly improves the charge transfer ability,reduces the ohmic impedance,enhances the intrinsic conductivity of the catalyst,and at the same time improves the electrophilicity of the active site,thus promoting the adsorption of nucleophilic intermediates,further improving the electrocatalytic activity of OER catalyst.