An Atomic‐Scale Explanation for The High Selectivity Towards Carbon Dioxide Reduction Observed On Liquid Metal Catalysts

The low-temperature liquid metals Ga-In and Ga-Sn have previously showcased >95 % selectivity towards the electrochemical reduction of CO₂ to formate, occuring only when the alloys are melted, not solid. Here, density functional theory molecular dynamics and metadynamics simulations reveal that CO₂ does not directly adsorb to the Ga-alloy surface, but instead is reduced indirectly by reaction with an adsorbed hydrogen. The reaction barrier is vastly more favourable when this process occurs at In or Sn sites (average: 0.26 eV), than when it occurs on Ga (average: 0.47 eV). However, there is no difference in barrier between solid and liquid surfaces. Instead, we find that H_ads is mobile only on the liquid surface, travelling due to the motion of the liquid beneath. This process drives H_ads to In/Sn sites, allowing low-barrier CO₂ reduction to occur only on the liquid. Therefore, the dynamic motion of liquid metal catalysts can underpin their unique reactivity. The result has far reaching implications for any protonation reaction conducted with a liquid metal catalyst.