Tunable Cu Enrichment Enables Designer Syngas Electrosynthesis from CO2. 
Using renewable energy to recycle CO2 provides an opportunity to both reduce net CO2 emissions and synthesize fuels and chemical feedstocks.  It is of central importance to design electrocatalysts that both are efficient and can access a tunable spectrum of products.  Syngas, a mixture of carbon monoxide (CO) and hydrogen (H2), is an important chemical precursor that can be converted downstream into small molecules or larger hydrocarbons by fermentation or thermochemistry.  Many processes that utilize syngas require different syngas compositions: we therefore pursued the rational design of a family of electrocatalysts that can be programmed to synthesize different designer syngas ratios.  We utilize in situ surface-enhanced Raman spectroscopy and first-principles density functional theory calculations to develop a systematic picture of CO* binding on Cu-enriched Au surface model systems.  Insights from these model systems are then translated to nanostructured electrocatalysts, whereby controlled Cu enrichment enables tunable syngas production while maintaining current densities greater than 20 mA/cm2.