Universal Surface Engineering of Transition Metals for Superior Electrocatalytic Hydrogen Evolution in Neutral Water
Journal of the American Chemical Society | 12 Aug 2017
B You, X Liu, G Hu, S Gul, J Yano, DE Jiang and Y Sun
The development of low-cost hybrid water splitting-biosynthetic systems that mimic natural photosynthesis to achieve solar-to-chemical conversion is of great promise for future energy demands, but often limited by the kinetically sluggish H2 evolu-tion reaction (HER) on the surface of nonprecious transition metal catalysts in neutral media. It is thus highly desirable to rationally tailor the reaction interface to boost the neutral HER catalytic kinetics. Herein, we report a general surface nitro-gen modification of diverse transition metals (e.g., iron, cobalt, nickel, copper, and nickel-cobalt alloy), accomplished by a facile low-temperature ammonium carbonate treatment, for significantly improved H2 generation from neutral water. Vari-ous physicochemical characterization techniques including synchrotron X-ray absorption spectroscopy and theory modeling demonstrate that the surface nitrogen modification does not change the chemical composition of the underlying transition metals. Notably, the resulting nitrogen-modified nickel framework (N-Ni) exhibits an extremely low overpotential of 64 mV at 10 mA cm-2, which is, to our knowledge, the best among those nonprecious electrocatalysts reported for H2 evolution at pH 7. Our combined experimental results and density functional theory calculations reveal that the surface electron-rich nitrogen simultaneously facilitates the initial adsorption of water via the electron-deficient H atom and the subsequent dis-sociation of the electron-rich HO-H bond via H transfer to N on the nickel surface, beneficial to the overall H2 evolution process.
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