Atomically Dispersed, Low-Coordinate Co-N Sites on Carbon Nanotubes as Inexpensive and Efficient Electrocatalysts for Hydrogen Evolution.

Hydrogen produced using renewable electricity is considered the key to achieving a low-carbon energy economy. However, the large-scale application of electrochemical water splitting for hydrogen evolution currently requires expensive platinum-based catalysts. Therefore, it is important to develop efficient and stable catalysts based on the rich reserves of transition metals as alternatives. In this study, the authors prepare a carbon-nanotube material enriched with atomically dispersed CoN sites having uniquely low coordination numbers via the simple mixing, pyrolysis, and leaching of inexpensive precursors. These atomically dispersed low-coordinate CoN sites provide an overpotential of only 82 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER) under challenging acidic conditions and show excellent durability in accelerated stability tests. Theoretical simulations also confirm that these unique, low-coordinate CoN2 sites have lower energy barriers in catalyzing the HER than Fe/NiN2 sites and commonly reported CoN3 /N4 sites. Therefore, the method provides a new concept for the design of single-atom catalytic sites with low coordination numbers. It also serves to reduce the cost of hydrogen production in the future owing to the high catalytic activity, low cost, and scalable production process.