| Hydrogen has the advantages of environmental protection,abundant resources,high heat of combustion.In many hydrogen production technologies,electrolysis of water is the safest and most reliable method,and it is widely used in industrial production.However,the presence of high overpotentials for hydrogen evolution in the electrolysis process has become the biggest problem which restricts its development.So the issue of finding electrode materials with high electrocatalytic activity and stability is imminent.In this paper,we composite metal Ni and three different nano-carbon materials to prepare Ni/rGO,Ni/NC,Ni/C3N4 and Ni/rGO/C3N4 composite electrodes by electrodeposition.The electrodes were analyzed by XRD,XPS,Raman,SEM,TEM and electrochemical analysis.The research contents are as follows:We design a catalytic material to co-electrodeposit Ni nanoparticles and reduced graphene oxide sheets on a three-dimensional Ni foam under supergravity field electrodeposition.When the concentration of graphene oxide in the plating solution is 1.0g L-1 and the electrodeposition time is 100 min,the catalyst exhibits excellent activity on hydrogen evolution with small overpotential of only 184 mV to drive 100 mA cm-2,a low Tafel slope(b=77 mV dec-1),a high exchange current density(j0=3.582 mA cm-2),and high stability.Such remarkable hydrogen evolution performance is attributed to good electrical conductivity,large specific surface area,superior interfacial density and harmonious synergistic effect between Ni particles and graphene sheets.In addition,density functional theory calculations explain that compared with pure Ni and graphene sheet,the Gibbs free energy of Ni/rGO composite is closer to zero.A nano nitrogen-doped carbon sphere?NC?material was prepared by a simple hydrothermal method,in which glucose was used as a carbon source and ethylenediamine was used as a nitrogen sourcethen.In addition,Ni/NC composite electrode was prepared by high-efficiency electrodeposition method.Compared with pure Ni and NC,Ni/NC composite electrodes have higher catalytic activity on hydrogen evolution.When the hydrothermal time is 6 h and the NC concentration is 0.2 g L-1,the prepared Ni/NC composite electrode presents the most excellent catalytic activity with small overpotential of 154 mV to acquire current density of 100 mA cm-2,a small Tafel slope of 79 mV dec-1,a much larger exchange current density of 2.020 mA cm-2 and superior stability in alkaline media.It benefits from the rich active sites,unique core-shell structure,good electrical conductivity and the synergistic effect between the Ni layers and NC.We find a quick and straightforward means to produce large-scale g-C3N4 which do not use template and easily get uniform nanostructures.Then,using the unique advantages of metal Ni,we prepared Ni/C3N4 and Ni/rGO/C3N4 non-precious metal composite catalysts by supergravity field electrodeposition using copper foil and nickel foam as substrates,respectively.Compared with traditional electrodeposition method,supergravity electrodeposition can enhance the mixing of materials,mass transfer and bubble separation during electrodeposition.This enables g-C3N4 and GO to be more uniformly embedded in the Ni-based electrode to form a special morphology and an increased specific surface area.The results show that Ni/C3N4 composite catalyst possesses coral-like structure and its unique morphology is in favour of electrochemical activity for hydrogen evolution.Simultaneously,the Ni/C3N4 composite catalyst presents prominent activity with small overpotential of 356 mV to reach current density of 100 mA cm-2,a high exchange current density of 1.91×10-4 A cm-2 and a low Tafel slope of 128 mV dec-1.The morphology of Ni/rGO/C3N4 composite electrode is thorn-like spheres.When the concentration of GO and C3N4 in the plating solution is 1.0 and 0.5 g L-1,respectively,the composite electrode presents excellent catalytic activity on hydrogen evolution with small overpotential of 109 mV to reach current density of 100 mA cm-2,which is superior to those of Ni-based compositions as well as other majority metal-free catalysts,and even rivals the electrocatalytic property of the state-of-the-art Pt/C catalyst.Density functional theory shows that there is a good synergy effect between Ni and g-C3N4 sheet,so that H*can reach the adsorption-desorption equilibrium on the Ni surface,thereby improving the catalytic activity of Ni for hydrogen evolution. |
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