Identified optimal cell design and operating conditions for efficient solar-driven electrochemical reduction of CO ₂ . Developed a method to predict polarization losses from the experimental data.

Significance: Chemical storage of solar energy can be achieved by electrochemical reduction of CO ₂ to CO and H ₂ , and subsequent conversion of this mixture to fuels. Identifying optimal conditions for electrochemical cell operation requires knowledge of the CO ₂ reduction mechanism and the influence of all factors controlling cell performance. We report a multiscale model for predicting the current densities for H ₂ and CO formation from first principles. Our approach brings together a quantum-chemical analysis of the reaction pathway, a microkinetic model of the reaction dynamics, and a continuum model for mass transport of all species through the electrolyte. This model is essential for identifying a physically correct representation of product current densities dependence on the cell voltage and CO ₂ partial pressure.

Population balance modeling is undergoing phenomenal growth in its applications, and this growth is accompanied by multifarious reviews. This review aims to fortify the model's fundamental base, as well as point to a variety of new applications, including modeling of crystal morphology, cell growth and differentiation, gene regulatory processes, and transfer of drug resistance. This is accomplished by presenting the many faces of population balance equations that arise in the foregoing applications.

Ammonia is an essential commodity chemical used in the manufacture of fertilizers, pharmaceuticals, ammunition, and plastics, and is a promising alternative fuel source and carrier. Today most ammonia is manufactured by the century-old Haber–Bosch process, which accounts for 1–2% of worldwide energy production and a substantial fraction of global greenhouse gas emissions. Solar-driven electrochemical synthesis of ammonia using nitrates presents a sustainable pathway to produce renewable fuels utilizing wastewater. Previous efforts in solar-driven electrosynthesis of ammonia have been seriously affected by lower specific activity (<10 mA cm⁻²) of electrochemical nitrate reduction reaction (NiRR) and thereby lower solar-to-fuel (STF) efficiency (<1%). Here, we show oxide-derived Co as an efficient NiRR catalyst with the highest specific activity (∼14.56 mA cm⁻² at −0.8 V vs. RHE) and selectivity. The oxide-derived Co offers a maximum faradaic efficiency of 92.37 ± 6.7% and ammonia current density of 565.26 mA cm⁻² at −0.8 V vs. RHE. Integrating this catalyst in a PV-electrolyzer cell yields an unprecedented STF efficiency of 11% for ammonia, which is an order of magnitude higher than state-of-the-art systems.