We have used computational quantum chemistry and atomistic thermodynamics to identify reaction intermediates for CO₂ electroreduction on partially reduced tin oxide electrodes. We find that a variety of different surface morphologies are thermodynamically accessible under reducing potentials with adsorbed CO₂, adsorbed H atoms, and O vacancy defects that represent partially reduced states. Our work supports prior conclusions from experimental findings that the active catalyst for this system is a hydroxylated and partially reduced SnO₂ surface that forms under operating conditions for CO₂ reduction. Employing thermodynamic descriptors and the computational hydrogen electrode model, we predict that doping Sn electrodes with Ti, V, Nb, or Zr will result in lower overpotentials for CO₂ reduction compared to undoped tin oxide.