(462h) Isopotential Electron Titration: Quantifying Hydrogen Metal-Adsorbate Charge Transfer

Shifting the binding energy of adsorbates by stabilizing metal-adsorbates bond formation via electrostatic work is one method to achieve dynamic catalysis. For example, catalytic condensers showed a shift in binding energy of CO to Pt via applied voltage [1]. This work establishes a technique to measure charge transfer enabling this electrostatic work at catalytically-relevant temperatures and pressures. The current was measured across Pt catalytic condensers as the gas composition in the vessel was switched between 1 atm and 0.005 atm H₂ (balance N₂) [2].

Figure 1A shows the current versus time while the composition was cycled. Switching to lower partial pressures resulted in a broad negative current peak while switching to higher partial pressure resulted in a narrow positive current peak. The integrations of these currents (i.e., charge) were equal and opposite in value and monotonically increased from 100 to 200 ^oC as shown in Figure 1B. Accounting for the change in coverages at each temperature using literature data [3], the amount of H* adsorbed/desorbed over the cycles was calculated. Figure 1C shows that the charge measured versus H* adsorbed/desorbed yielded a linear correlation, suggesting that each H* adsorption event donated 0.19% of an electron to the Pt surface. This extent of charge transfer allows us to calculate the change in binding energy for a given catalyst surface voltage drop. The isopotential titration technique can be used to measure the extent of charge transfer for a range adsorbates and catalysts allowing researchers to predict the effects of dynamic voltages on catalyst surface coverages.

[1] Onn., T.M., et al. J. Am. Chem. Soc. 144, 48 (2022)

[2] Hopkins, J., Page, B., et al. ChemRxiv (2025)

[3] García-Diéguez, M., et al. J. Phys. Chem. C 123, 12 (2019)