Yu Xiangtao, Yang Jun, Ren Xiangyu, Sui Zhuyin
Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China.
School of Chemistry & Chemical Engineering, Yantai University, Yantai 264005, China.
Membranes (Basel). 2021 Feb 27;11(3):165. doi: 10.3390/membranes11030165.
The structure of Ni films is essential to their electrocatalytic performance for hydrogen evolution reaction (HER). The pH value and EDTA (ethylene diamine tetraacetic acid) additive are important factors for the structure control of electrodeposited metal films due to their adjustment of metal electrocrystallization and hydrogen evolution side reactions. The structures of Ni films from 3D (three-dimensional) porous to compact and flat structure are electrodeposited by adjusting solution pH values or adding EDTA. It is found that when pH value increases from 7.7 to 8.1, 3D porous films change to compact films with many protrusions. Further increasing the pH value or adding 0.1 M EDTA causes compact and flat films without protrusions to appear. When pH ≤ 7.7, hydrogen bubbles with large break-off diameter are easily adsorbed on film surface acting as porous structure templates, and the electroactive ion species, Ni and Ni(NH) complexes with low coordination number ( ≤ 3), possess high reduction overpotential, which is beneficial to forming protrusions and smaller particles. So, porous Ni films are electrodeposited. In solutions with pH ≥ 8.1 or 0.1 M EDTA, Ni(NH) complexes with high coordination number (6 ≥ ≥ 3) and hexadentate chelate are formed. Due to the improved wettability, bubbles with a small break-off diameter rapidly detach the film surface resulting in strong stirring. The reduction overpotential is reduced, leading to the formation of larger particles. Therefore, the solution leveling ability increases, and it is difficult to form protrusions, thus it forms a compact and flat film. The 3D porous film exhibits excellent catalytic performance for HER due to the large catalytic activity area.
镍膜的结构对其析氢反应（HER）的电催化性能至关重要。pH值和乙二胺四乙酸（EDTA）添加剂是电沉积金属膜结构控制的重要因素，因为它们能调节金属电结晶和析氢副反应。通过调节溶液pH值或添加EDTA，可电沉积出从三维（3D）多孔结构到致密平整结构的镍膜。研究发现，当pH值从7.7增加到8.1时，3D多孔膜会转变为带有许多凸起的致密膜。进一步提高pH值或添加0.1 M EDTA会导致出现无凸起的致密平整膜。当pH≤7.7时，具有较大脱离直径的氢气泡容易吸附在膜表面，充当多孔结构模板，且具有低配位数（≤3）的电活性离子物种镍和镍氨络合物具有较高的还原过电位，这有利于形成凸起和更小的颗粒。因此，会电沉积出多孔镍膜。在pH≥8.1的溶液或含有0.1 M EDTA的溶液中，会形成高配位数（6≥≥3）的镍氨络合物和六齿螯合物。由于润湿性提高，具有较小脱离直径的气泡会迅速从膜表面脱离，导致强烈搅拌。还原过电位降低，导致形成更大的颗粒。因此，溶液的整平能力增强，难以形成凸起，从而形成致密平整的膜。3D多孔膜由于具有较大的催化活性面积，对析氢反应表现出优异的催化性能。
