The oxygen evolution reaction (OER) of electrochemical water splitting is the key process in solar-to-chemical conversion technologies, but the kinetics of OER is sluggish, even when facilitated by high-efficiency precious-metal-containing catalysts. Therefore, it is very important to explore high-activity, robust-stability, and low-cost catalysts. In general, the activities of metal compounds based OER catalysts mainly originates from their intrinsic metallicity and the excellent activity of the oxidized layer species after in situ surface reconstruction. Hua Gui Yang’s Group of East China University of Science and Technology designed and synthesized a highly efficient and stable water-splitting catalyst and conducted in-depth research on the in-situ reconstruction during OER process. Their research has been published on the 6th issue of Materials Horizons in 2019.

The researchers used Mo₆Ni₆C as a precursor to prepare OER catalyst by in situ electrochemical treatment. The research indicates that the Mo₆Ni₆C large cells broke into nanoclusters of carbon interconnected MoNi alloys after the reconstruction, the metallic characteristics could boost the charge transfer process and the small size could expose more active sites. At the same time, they also found that the carbon in the crystal structure of Mo₆Ni₆C was converted into amorphous, which could improve poor charge transport caused by the gaps between nanoclusters. Furthermore, the MoNi alloys would get oxidized on the surface to form Mo6+ incorporated NiOOH species during the pre-oxidation process, so the OER activity of the material could be further activated.

The structural transformation of Mo6Ni6C in the electrochemical process was revealed by XAFS carried out at 1W1B-XAFS station of BSRF. The results in Figures A and C show that the metallic Ni changed to oxidized Ni during OER process, with the disappearance of Ni-Ni bonds and the formation of Ni-O bonds. The results in Figure B and D show that as the applied potential and time increased, Mo gradually changed to the oxidized state, and the Mo-Mo bonds gradually decreased while the Mo-O bonds gradually increased.

Mo₆Ni₆C has been demonstrated as a high-performance and low-cost precatalyst for OER in this research. An efficient water electrolyzer was demonstrated by using Mo₆Ni₆C as both anode and cathode material, achieving a j of 10 mA cm^-2 at 1.47 V when continuously working for more than 200 h. With the help of synchrotron radiation, the research team further tracked the changes of the material during the in-situ electrochemical process, and revealed the reasons for the high performance of the material, which can provide a reference for the large-scale application of electrochemical energy-conversion devices.

Article:

Meng Yang Zu, Chongwu Wang, Le Zhang, Li Rong Zheng and Hua Gui Yang* Reconstructing bimetallic carbide Mo₆Ni₆C for carbon interconnected MoNi alloys to boost oxygen evolution electrocatalysis. Materials Horizons 6(2019), 115-121.