Dual Function of Hypo-d-electronic Transition Metals in the Brewer Intermetallic Phase for the Highly Efficient Electrocatalytic Hydrogen Evolution Reaction in Alkaline Electrolytes
Yuqing Yang, Shen-Jing Ji, Nian‐Tzu Suen
Abstract
Reported are the synthesis, material characterization, and electrocatalytic hydrogen evolution reaction (HER) in acid and alkaline electrolytes for the Brewer intermetallic phase, Nb 6 Co 7 and Mo 6 Co 7 . It was realized that the overpotential at a current density of 10 mA/cm 2 (η 10 ) for Nb 6 Co 7 (η 10 = 62 mV) and Mo 6 Co 7 (η 10 = 143 mV) are both much lower than that of using a single Co metal (η 10 = 253 mV) in alkaline electrolytes. The enhancement of electrocatalytic HER activity of Nb 6 Co 7 and Mo 6 Co 7 can be attributed to the hypo-hyper-d-electronic interaction between Nb/Mo and Co elements. Based on the result of density functional theory calculation, alloying between Nb/Mo and Co elements will increase the antibonding state population of the Co–Co bond near the Fermi level ( E F ), which induces the synergistic effect to influence the adsorption energy of the H atom (Δ G H ) on the surface of Nb 6 Co 7 and Mo 6 Co 7 . Moreover, the role of the Nb element is not only a simple electron donor but is also an anchor position for the OH molecule (i.e., dual function) due to the bonding character of the Nb–Co bond near E F . It can reduce the OH position effect as well as the activation energy for water dissociation, which rationalizes the high and robust HER performance of Nb 6 Co 7 to that of commercial Pt/C (η 10 = 67 mV) in alkaline electrolytes.