大气等离子喷涂制备梯度多孔电极及其碱式电解水性能研究

The Preparation and Performance of Gradient Porous Electrodes Obtained via Atmospheric Plasma Spraying Used in Alkaline Water Electrolysis

目的探索电极的梯度多孔结构对碱式电解水析氢性能的影响。方法采用大气等离子喷涂工艺制备不同Al含量的涂层,经化学腐蚀后,得到单一多孔电极和梯度多孔电极。通过SEM/EDS、XPS、XRD和工业CT对样品微观形貌、元素价态、物相等进行表征和分析,采用线性扫描伏安法(LSV)、循环扫描伏安法(CV)和电化学阻抗谱法(EIS)等手段研究样品的析氢性能。结果通过控制Al的添加量,可以有效控制涂层的孔隙率。通过多组粉末的配合喷涂,成功实现了梯度多孔结构的制备。所制备样品的析氢Tafel斜率都接近于120 mV/dec,其析氢速率控制步骤皆为Volmer过程,即水分子吸附和解离过程。N30A表面最平整,表现出最接近电容的阻抗特性,其电解性能也因此最差;N40A表现出与N50A类似的阻抗特性,但其整体孔隙率较低,因此其电解性能较差;低电流密度下,N50A和N543A表现出十分接近的电解性能,而高电流密度下N543A表现出更加优越的电解性能。结论梯度多孔结构的引入可以促进电解液的输运,同时提供较好的排气能力,又能保证足够的反应活性位点,因此可以有效提升析氢性能。

This paper aims to explore the effect of electrode structure on hydrogen evolution performance during alkaline water electrolysis.By preparing a gradient-arranged porous structure,the contradictory problems existing in the specific surface area and mass transfer and transport of a single porous structure can be effectively balanced,achieving a more optimistic hydrogen evolution effect.In this paper,spraying powders with Al content of 30vol%,40vol%and 50vol%were obtained by mixing Ni powder and Al powder.Then four kinds of coating powders of N30A,N40A,N50A,and N543A were prepared by atmospheric plasma spraying with the prepared powders respectively,wherein the N543A coating was prepared by spraying N50A,N40A,and N30A powders in turn.After chemical etching,four groups of porous coatings were successfully obtained.The 2D and 3D microscopic morphology of the sample were characterized by SEM and industrial CT.EDS,XPS and XRD showed the element valence state and phase composition of the sample.The hydrogen evolution properties of the samples were investigated and compared by electrochemical test methods such as linear sweep voltammetry(LSV),cyclic sweep voltammetry(CV),and electrochemical impedance spectroscopy(EIS).The experimental results show that the porosity of the coating can be effectively controlled by controlling the addition amount of Al,and a loose and porous electrode structure can be obtained;Through the coordinated spraying of multiple groups of powders,the preparation of the gradient porous structure was successfully achieved.All electrodes showed good stability with no obvious attenuation before and after the test.In terms of the reaction mechanism,the control steps of the hydrogen evolution rate of the prepared samples are all Volmer processes,that is,the adsorption and dissociation process of water molecules.The change of aluminum content and the construction of the gradient coating did not significantly change the reaction mechanism.N30A has the smoothest surface,showing the impedance characteristics closest to the capacitor,therefore its electrolytic performance is the worst;N40A shows similar impedance characteristics to N50A,but its overall porosity is lower,so its electrolytic performance is poor;At low current density,N50A and N543A showed very close electrolytic performance while N543A showed more superior electrolytic performance at high current density,Combined with the results of its three-dimensional structure analysis,it can be seen that the three-dimensional porosity of N50A is higher than that of N543A,and it can provide better exhaust capacity during electrolysis,but the corresponding surface area or active sites are reduced,resulting in a higher hydrogen evolution overpotential at a higher current density.Due to the porous structure of the N543A sample,the gas generated by electrolysis can be effectively extracted,so it still shows better electrolytic performance than N50A when the porosity is lower than that of N50A.The introduction of the gradient porous structure can not only promote the transport of the electrolyte,but also provide better exhaust capacity and ensure sufficient reactive sites,so it can effectively improve the hydrogen evolution performance.