Wireless potentiometry of thermochemical heterogeneous catalysis

Catalyst surfaces in contact with liquid media are subject to spontaneous charge transfer reactions that electrically polarize the solid-liquid interface. Consequently, the electrochemical potential, Ecat, of the surface is a critical parameter that defines the free-energy landscape of catalysis. Ecat can be readily measured for a catalyst supported on a conductive material and wired to an external circuit but is difficult to quantify for the vast majority of thermochemical catalysts that are supported on electrical insulators. This measurement gap has impeded a unifying understanding of the role of electrochemical polarization in thermochemical catalysis. Herein, we develop a methodology for quantifying Ecat of metal catalysts supported on insulators by introducing a small concentration of a redox-active molecule to establish a wireless electrical connection between the dispersed catalyst and an inert sensing electrode. We validate this approach by quantifying Ecat during catalytic reactions involving H2 or O2 in water and acetonitrile solvent. Using this methodology, we expose distinct rate-potential scalings for aerobic formic acid oxidation catalysis on SiO2- and Al2O3- versus TiO2-supported Pt catalysts. The methodology we develop herein enables the broad-based investigation of the role of electrochemical polarization in thermochemical catalysis.