One strategy to reduce global CO2 emissions calls for capturing the greenhouse gas and converting it electrochemically to fuels and chemicals. Scientists working toward that goal recently found that CO2 can be converted with little energy input to formic acid, formaldehyde, and methanol on a platinum electrode in an acidic solution of pyridine. Yet a detailed understanding of the reaction mechanism, which could hasten progress in that area, remained elusive. Mehmed Z. Ertem of Brookhaven National Laboratory, Victor S. Batista of Yale University, and coworkers have now used computational techniques to sort out the mechanism. The team proposes that CO2 is reduced by Pt-bound H atoms in the form of hydrides. These species migrate from the electrode surface to CO2 in a proton-coupled hydride transfer mechanism that is activated by acidic pyridinium ions, PyrH+. Surfacebound H atoms consumed by the process are replenished by the one-electron reduction of PyrH+ through proton-coupled electron transfer (J. Phys. Chem. Lett., DOI: 10.1021/jz400183z). The mechanism depends on the presence of PyrH+, which is essential for providing a high concentration of Brønsted acid in contact with the Pt surface and for activating CO2 during hydride transfer, the team says.