The Science of Artificial Photosynthesis: Replacing Harmful, Inefficient and Unwanted Biofuels, Now

The large-scale cultivation of energy crops is the greatest threat to Earth’s ecosystems and human survival in the near term. The measured solar to biomass energy conversion efficiency of plantation grown sugarcane and palm oil - the recoverable absorbed energy - ranges from 0.20% to 0.88% and the solar to biofuel efficiency is 0.1% and 0.23%. Contrast this to photovoltaic and wind solar conversion to electricity of > 18%. I will highlight the design principles of electrocatalysts for reducing CO2 to various C1 to C4 products using water as hydrogen source (aka, Artificial Photosynthesis). Using anaerobic enzymes as blueprint, we have predicted, synthesized and tested six nickel phosphide compounds and their isostructural alloys doped with Fe. Individual NixPy compounds achieve unprecedent electrical conversion efficiencies to C1-C4 products (93-99%). The product selectivity can be tuned through addition of acid-base co-catalysts to steer intermediates to desired products. The chemical mechanism of catalysis has been revealed using surface spectroscopies and density functional calculations. Independent efforts at scaling-up the technology to make C2 alcohols is underway and offers a potential >16% net solar to fuel conversion efficiency.