Isotope-Labeling Studies in Water Oxidation Electrocatalysis

Abstract

Improving understanding of the electrocatalytic mechanisms for the oxygen evolution reaction (OER) will help in designing electrode materials with lower catalytic overpotential and greater stability, increasing the efficiency and economic viability of electrolysis. Isotope-labeling can be a powerful tool for elucidating catalytic mechanisms, including in electrocatalysis. Herein, we apply 18-O labeling, utilizing a fully quantitative electrochemistry - mass spectrometry method with unprecedented sensitivity[1] and post-characterization by low-energy ion scattering spectrometry, to investigate the electrocatalytic mechanism of oxygen evolution. Nickel-iron based electrodes are used in industrial alkaline water electrolysis, but questions remain about the intrinsic activity and electrocatalytic mechanism. By performing a series of isotope-labeling experiments on a model system of mass-selected Ni-Fe nanoparticles, we show that oxygen evolution does not proceed via lattice oxygen exchange and that only the surface of the nanoparticles are active[2]. This allows us to estimate the turn-over frequency of the active sites, 6 O2 molecules per site per second, which is higher than previous estimates. We also quantify lattice oxygen exchange in IrO2 and RuO2 thin films during oxygen evolution in acidic electrolyte as a function of electrochemical roughening, and perform oxygen stripping experiments to probe OER intermediates. This talk will describe these findings and further explore the potential of isotope labeling studies in electrocatalysis. [1] D. B. Trimarco, S. B. Scott et al, Enabling real-time detection of electrochemical desorption phenomena with sub-monolayer sensitivity. Electrochimica Acta. 2018, 268, 520-530 [2] C. Roy, B. Sebok, S. B. Scott et al, Impact of nanoparticle size and lattice oxygen on water oxidation on NiFeOxHy. Nature Catalysis. 2018, 1(11), 820–829 Figure 1