Assuming a Langmuir adsorption model, the equilibrium adsorption coefficient (Kads) is proportional to the ratio of coverage and concentration; greater coverage at lower concentration-observed here for CeO2-δ relative to SnO2-yields a larger Kads. As Kads increases, Δ𝐺 𝑎𝑑𝑠 becomes more negative (more favorable adsorption), indicating that nitrate has a greater affinity towards CeO2-δ than SnO2 (Δ𝐺 𝑎𝑑𝑠,𝐶𝑒𝑂 2 < Δ𝐺 𝑎𝑑𝑠,𝑆𝑛𝑂 2 ). This suggests that for a given nitrate concentration, nitrate will be present at higher coverages on the Cu/CeO2-δ electrode (or perhaps bound more strongly relative to competitively adsorbed hydrogen at HER-relevant potentials), promoting greater NO3RR activity relative to Cu/FTO (Figure ).