Intermetallic Alloys as CO Electroreduction Catalysts-Role of Isolated Active Sites

One of the main challenges associated with the electrochemical CO or CO₂ reduction is poor selectivity toward energetically rich products. In order to promote selectivity toward hydrocarbons and alcohols, most notably, the hydrogen evolution reaction (HER) should be suppressed. To achieve this goal, we studied intermetallic compounds consisting of transition metal (TM) elements that can reduce CO (Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) separated by TM and post transition metal elements (Ag, Au, Cd, Zn, Hg, In, Sn, Pb, Sb, and Bi) that are very poor HER catalysts. In total, 34 different stable binary bulk alloys forming from these elements have been investigated using density functional theory calculations. The electronic and geometric properties of the catalyst surface can be tuned by varying the size of the active centers and the elements forming them. We have identified six different potentially selective intermetallic surfaces on which CO can be reduced to methanol at potentials comparable to or even slightly positive than those for CO/CO₂ reduction to methane on Cu. Common features shared by most of the selective alloys are single TM sites. The role of single sites is to block parasitic HER and thereby promote CO reduction.