  Copper is a good CO2 electroreduction catalyst as products beyond CO form,
but efficiency and selectivity is low. Experiments have shown that admixture of
other elements can help, and computational screening studies have pointed out
various promising candidates based on the adsorption of a single CO molecule as
a descriptor. Our calculations of CO adsorption on surfaces where a first row
transition metal atom replaces a Cu atom show that multiple CO molecules, not
just one, bind to the substitutional atom. For Fe, Co, and Ni atoms, a decrease
in binding energy is found, but the reverse trend, namely increasing bond
strength, is found for V, Cr, and Mn and the first three CO molecules. Magnetic
moment, charge, and position of the substitutional atom are also strongly
affected by the CO adsorption in most cases. Magnetic moment is stepwise
reduced to zero, and the outward displacement of the substitutional atom
increased.
