Non-Noble Metal-Based Electrocatalysts for Efficient Hydrogen Evolution Reactions

Electrolysis of water by electricity generated from renewable energy sources is promising sustainable hydrogen (H2) production method. A critical task to realize the widespread application of this method is to develop high performance, low price, and stable electrocatalysts for hydrogen evolution reaction (HER). This thesis focuses on the understanding of the stability of non-noble metal-based electrocatalysts in electrolytes with a wide range of pH and the development of novel high-performance non-noble metal-based electrocatalysts for HER. First, using Ni2P as a reprehensive 3d transition metal-based electrocatalyst, its pHdependent performance stability was studied in detail. The pH of electrolytes strongly influences the HER activity of the Ni2P electrocatalyst. Tests in 19 electrolytes with pH ranging from 0.52 to 13.53, my results show that Ni2P is much more active in acidic and alkaline electrolytes. With the increase of pH, lower H+ concentration reduces the formation of adsorbed H atoms in the Volmer reaction, resulting in more impoverished activities. However, the high activity observed in the strong alkaline electrolytes is not the intrinsic property of Ni2P. Ni oxides/hydroxides are formed in strong alkaline electrolytes under applied potentials, resulting in improved activities. Next, I demonstrated the synthesis of ultrafine β-Mo2C nanoparticles with narrow size distribution (2.2 ± 0.3 nm) and high mass loading (up to 27.5 wt.%.) on graphene substrate using a giant Mo-based polyoxomolybdate (POM) cluster, Mo132 ((NH4)46[Mo132O372(H2O)72(CH3COO)30]). A nitrogen-containing polymeric binder (polyethyleneimine) was used to create Mo-N bonds between Mo2C nanoparticles and nitrogen-doped graphene layers, which dramatically improve the catalytic performance of the Mo2C electrocatalyst for HER as revealed by X-ray photoelectron spectroscopy and density functional theory calculations. The optimized Mo2C electrocatalyst shows a large exchange current density of 1.19 mA cm–2, a high turnover frequency of 0.70 s–1 as well as excellent durability. This new synthesis strategy opens the possibility of developing practical platinum substitutes based on Mo2C for practical HER applications