(Invited) Electrocatalyst Development for Efficient CO₂ Electrolysis

This talk will discuss recent efforts at the National Energy Technology Laboratory (NETL) to develop efficient electrocatalysts that convert CO2 and water into C1 products, such as carbon monoxide (CO) and formic acid (HCOOH). The first example combines advanced surface science techniques, computational modeling, and electrochemical evaluation to track the size-dependent CO2 reduction vs. HER selectivity of silver nanocatalysts with sub-nanometer resolution. Understanding size-dependent catalytic properties is important to maximize the utilization of costly, state-of-the-art catalyst materials. Experimental efforts synthesized and evaluated Ag nanocatalysts with controlled diameters between 2-6 nm, and we identified ~4 nm Ag particles as the optimum balance of activity, selectivity, and catalyst utilization. Computational modeling techniques, including DFT, transition state theory, and microkinetic modeling identified key catalytically active surface sites that were responsible for HER vs. CO2 reduction, determined the respective active sites’ population as a function of particle size, and then predicted HER vs. CO2 reduction rates and selectivity for Ag nanocatalyst with diameters between 1-10 nm. Our computational results predicted ~4 nm particle provided the highest combination of product selectivity, catalyst utilization, and catalytic activity based on a total metal basis, which was in near perfect agreement with experiential results. These experimental and computational results should guide future catalyst design efforts by placing a lower bound on the size of practical Ag catalysts. A second example will highlight efforts to develop 3D structured and chemically-doped SnO2 catalysts for the conversion of CO2 into formate and formic acid. We coupled novel synthetic techniques with advanced synchrotron characterization, computational modeling, and evaluation MEA-style electrolyzer devices. In the case of 3D structured SnO2 catalysts we found CO2 conversion activity was substantially improved by increasing the electrocatalytically active surface area, while doping SnO2 catalysts with heteroatoms created new active sites that lowered the CO2 conversion overpotential and boosted performance.