泡沫基材-Ni-石墨烯复合镀层制备及电催化析氢性能研究

Preparation and Electro-catalytic Hydrogen Evolution Performance of Foam Substrate-Ni-Graphene Composite Coating

目的 采用电沉积技术在泡沫基材上沉积制备Ni-石墨烯复合镀层,期望借助泡沫基材的三维多孔结构和石墨烯的超高比表面积来改变复合材料的表面状态,进而获得高镀层的电催化析氢性能。方法 采用电沉积技术将石墨烯作为第二相粒子沉积,制备了泡沫基材-Ni-石墨烯复合电极,通过SEM和EDS研究了其微观形貌及成分,并利用电化学工作站完成了镀层电极的极化曲线、交流阻抗和电解水稳定性测试,使用控制变量法探究了镀层厚度、镀液石墨烯浓度和基材形貌对镀层电催化析氢活性的影响。结果 SEM和EDS表征发现,镀层表面形貌受镀液中石墨烯浓度影响较大,石墨烯作为第二相嵌入镀层后,明显改变了复合镀层的表面形貌,其存在形态为颗粒状,在150 mg·L^(–1)时颗粒堆积最多。进一步利用电化学分析技术探究了镀层厚度、镀液石墨烯浓度和基材形貌对电极电催化析氢性能的影响,发现在一定范围内,不同厚度镀层的电催化析氢活性基本相同;石墨烯质量浓度为150mg·L^(–1)时制得的电极的电催化析氢性能最优,析氢过电位为211.2m V(vs.RHE),且电解水稳定性良好;泡沫基材镀层的电催化析氢活性明显优于平板基材镀层。结论 石墨烯的引入和泡沫基材三维多孔结构均增大了复合镀层的比表面积,是电极表现良好的电催化析氢活性的关键。

In this paper,the foam substrate-Ni-graphene composite electrode was prepared by depositing graphene as the second phase particle on the foam substrate.The concentration gradient of graphene was 0 mg·L^(–1),50 mg·L^(–1),10 mg·L^(–1),150 mg·L^(–1),200 mg·L^(–1),and 250 mg·L^(–1).It was expected to change the surface state of the composite material with the three-dimensional porous structure of the foam substrate and the ultra-high specific surface area of the graphene,so as to obtain the electrocatalytic hydrogen evolution performance of the high coating.After graphene was embedded as the second phase coating,the surface morphology of the composite coating was obviously changed,and its existence form was granular.At a magnification of 2 000,the coating surface had a particle diameter of about 1 μm.With the increase of the concentration of graphene,the particle distribution density gradually increased first and then decreased,and the particle size became larger.The particle accumulation was the highest at the graphene concentration of 150 mg·L^(–1).Combined with the summary table of EDS composition analysis,it was found that with the increase of graphene concentration,the carbon content in the coating solution increased,and the C content in the composite coating gradually increased,with the highest concentration of 200 mg·L^(–1),and then 250 mg/L was slightly reduced.At the same time,with the increase of graphene concentration,the Ni content gradually decreased,and the Fe content was negligible.It showed that the composite coating could cover the substrate surface well and be thicker.The polarization curve and Tafel slope curve indicated that the reaction pathway of hydrogen evolution reaction(HER) with composite coating was Volmer-Heyrovsky,and the electrocatalytic adsorption step was the reaction control step.The coating prepared at 150 mg·L^(–1) had the lowest Tafel slope,which was 105.3 mV·dec^(–1).And the hydrogen evolution potential of composite coating with graphene was lower than that of coatings without graphene.At a current density of 10 mA·cm^(–2),the coatings prepared at 150 mg·L^(–1) had the lowest hydrogen evolution overpotential.AC impedance map showed that the arc resistance diameter of the Ni base graphene composite coating was less than that of the graphene-free Ni coating.Combined with the fitting data and relevant theories,the electrochemical surface area(ESCA) of the coatings joined with graphene was higher than that without graphene,and graphene increased the ESCA on the coating surface,thus improving the electrocatalytic hydrogen evolution activity of the coated electrode.In addition,the effects of coating thickness and substrate morphology on electrode electrocatalytic hydrogen evolution performance were explored.And it was found that the electrocatalytic hydrogen precipitation activity of different thickness composite coatings were basically the same.The electrocatalytic hydrogen evolution activity of foam substrate coating was significantly better than that of plate substrate coating.The timing potential test of the foam substrate-Ni-Graphene composite coating electrode at 100 mA·cm^(–2) constant current density showed that the initial potential of the coating electrode was about –1.48 V(vs.SCE),and the potential dropped to about –1.50 V in the first 1 000 s,the fluctuation was slightly obvious,not stable in the early stage.The fluctuation of the potential in the rest of the time was not large.The change value was only 0.01 V,and the curve was flat.It showed that the electrode electrolysis had good water stability.In conclusion,the introduction of graphene and three-dimensional porous structure of the foam substrate increase the specific surface area of the composite coating,which is the key to the good electrocatalytic hydrogen evolution activity of the electrode.