Atomically precise, inherently charged Au-25 clusters are an exciting prospect for promoting catalytically challenging reactions, and we have studied the interaction between CO2 and Au-25. Experimental results indicate a reversible Au-25-CO2 interaction that produced spectroscopic and electrochemical changes similar to those seen with cluster oxidation. Density functional theory (DFT) modeling indicates these changes stem from a CO2-induced redistribution of charge within the cluster. Identification of this spontaneous coupling led to the application of Au-25 as a catalyst for the electrochemical reduction of CO2 in aqueous media. Au-25 promoted the CO2 -> CO reaction within 90 mV of the formal potential (thermodynamic limit), representing an approximate 200-300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO2 conversion occurred at -1 V (vs RHE) with approximately 100% efficiency and a rate 7-700 times higher than that for larger Au catalysts and 10-100 times higher than those for current state-of-the-art processes.