Phosphorene-Supported Transition-Metal Dimer for Effective N2 Electroreduction.

The electrochemical reduction of N2 to NH3 at ambient conditions is a promising alternative to the energy-intensive, high-temperature, high-pressure Haber-Bosch process. But it is extremely challenging to find an electrocatalyst that can effectively activate N2 and reduce it to NH3 . From first principles density functional theory, we found that the Ti dimer supported on single-layer phosphorene can be used as a promising electrocatalyst for N2 capture and conversion to NH3 . The overpotential (relative to the standard hydrogen electrode) was found to be as low as 0.20, much lower than those predicted on the Ti surface (1 to 1.5 V) or their nitrides (0.5 to 1 V). In addition, we found that hydride is involved in the N2 reduction on the Ti dimer catalyst via formation of Ti2 -H species, and the hydride would favorably transfer onto the adsorbed N2 * to form *NNH intermediate and further reduced to NH3 . Moreover, we also examined other first-row transition metal dimers, and found that Sc and Fe dimer to be potential catalysts which could catalyze N2 reduction at a low overpotential of about 0.21 and 0.45 V, respectively. Our predictions hence suggest Ti, Sc and Fe dimer clusters supported on phosphorene as promising electrocatalysts for N2 reduction to NH3 .