Electrocatalytic hydrogen evolution reaction is an efficient approach for producing hydrogen fuel combining with the renewable energy. The large-scale application of platinum-based catalysts are severely restricted due to the high cost and limited reserves. In recent decades, researchers have made tremendous contributions in reducing catalyst costs, increasing catalytic activity and improving stability. Plentiful non-noble metal-based catalysts have been developed, but most non-noble metal-based catalysts have difficulty meeting the operating conditions over whole pH range. The pH change surrounding the catalyst during the electrocatalytic hydrogen evolution reaction can easily cause the activity decay or even death. Herein, Prof. Sun's group in Beijing University of Chemical Technology combined amorphous ruthenium sulfide (the price of ruthenium is only 1/3 of platinum) with graphene to develop a Pt-like activity electrochemical HER catalyst, which can work very well in acidic, neutral and alkaline solutions. It also can effectively resist the pH change during the catalytic process. The relevant results were published as an inside cover in the Small journal on September 17, 2019: https: / /doi.org/10.1002/smll.201904043.

This research group used a simple hydrothermal method to achieve the uniform loading of amorphous ruthenium sulfide nanoparticles on the graphene. Since ruthenium sulfide is amorphous, it is long-range disordered and short-range ordered, which is more conducive to the exposure of the active site for catalyzing. Electrochemical studies have shown that it possesses a similar catalytic activity to Pt catalyst in acidic, neutral and alkaline environments, even slightly better than Pt/C under neutral conditions. Since amorphous ruthenium sulfide can tolerate the pH change and equips with the protection of three-dimensional coiled structure of graphene, it exhibits excellent electrocatalytic stability at high current density. There is almost no performance degradation after 12 hours long-term operation at an initial current density of 50 mA/cm². Based on the Tafel slope analysis, the authors found that the as-prepared catalyst carried out the Volmer-Heyrovsky mechanism to catalyze HER, which was a single-site catalytic mechanism. The DFT calculation also shows that the ruthenium sulfide-based catalysts with isolated active site have neither strong nor weak adsorption capacity for H.

Using XAFS experiment carried out at 1W1B-XAFS station of Beijing Synchrotron Radiation Facility (BSRF), the author conducted a detailed study on the coordination of ruthenium before and after hydrogen evolution reaction. In the initial structure, there are Ru-S and Ru-S-S coordination signals, but after the hydrogen evolution reaction test, only the first shell of Ru-S can be detected. There is no any second shell coordination, as well as no coordination like Ru-Ru and Ru-O-Ru, so it can be speculated that the distance between two Ru atoms in RuSx is relatively long. Ru, as active site, tends to complete the single-site catalytic process. The authors say that the synchrotron radiation analysis provides a great help in confirming the single-site catalytic mechanism.

In summary, this work provides a new insight into the catalytic mechanism of amorphous material when it comes to electrocatalytic HER. The method of preparing catalysts in this work is simple and easy to industrialized application.

Article:

Pengsong Li, Xinxuan Duan, Shiyuan Wang, Lirong Zheng, Yaping Li, Haohong Duan*, Yun Kuang* and Xiaoming Sun*. Amorphous Ruthenium-Sulfide with Isolated Catalytic Sites for Pt-like Electrocatalytic Hydrogen Production Over Whole pH Range. Small 2019, 15, 1904043.