Global climate change and energy concerns have led to a surge of interest in the electrochemical conversion of carbon dioxide (CO2) to fuels such as methane and ethanol. Metals such as copper, tin, gold, and others have proven effective as catalysts for reducing CO2 to a wide spectrum of products. Interestingly, it has recently been shown that oxidizing some of these metals further enhances their catalytic activities and selectivities. Oxidation seems to play a fundamental, but poorly understood, role in modulating the reactivity of these catalysts. In this Review, recent progress towards understanding the effect of oxygen, surface morphologies, and local pH gradients on the catalysis of CO2 reduction is discussed.

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