Tracking Electrical Fields at the Pt/H₂O Interface during Hydrogen Catalysis

Abstract

We quantify changes in the magnitude of the interfacial electric field under the conditions of H2/H+ catalysis at a Pt surface. We track the product distribution of a local pH-sensitive, surface-catalyzed nonfaradaic reaction, H2 addition to cis-2-butene-1,4-diol to form n-butanol and 1,4-butanediol, to quantify the concentration of solvated H+ at a Pt surface that is constantly held at the reversible hydrogen electrode potential. By tracking the surface H+ concentration across a wide range of pH and ionic strengths, we directly quantify the magnitude of the electrostatic potential drop at the Pt/solution interface and establish that it increases by ∼60 mV per unit increase in pH. These results provide direct insight into the electric field environment at the Pt surface and highlight the dramatically amplified field existent under alkaline vs acidic conditions.

Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions

“…Indeed, the pH-dependence of electrocatalytic reactions has been and remains a subject of vigorous research. 45,39,46,47,48,49,50,51,52 In these studies, researchers have invoked pH-dependent adsorption energies 48,51 , electric field strengths 45,50,52 , potentials of zero charge 45,49,50 , and water reorganization barriers 45 as contributions to the pH-dependence of a variety of half-reactions. Our studies imply that those same effects, with the additional contribution of varying mixed potentials, are relevant for thermochemical catalysis as well.…”

Caffeinated Interfaces Enhance Alkaline Hydrogen Electrocatalysis

“…We have showed in our previous works that OHad is not an active participant in the hydrogen reactions and any effect it has on HER/HOR kinetics may be indirect [16][17][18] . Another prominent school of thought hypothesizes that the electrostatic interaction of water dipoles with the electric field influences water reorganization kinetics and can explain the pH dependence 9, 19,20 . While there is good evidence that the electric field is stronger at high pH than at low pH, a direct link between field strength and water dynamics remains to be proven.…”

“…However, several groups have recently highlighted the fact that thermodynamic adsorption energies alone are insufficient to fully describe the HER/HOR kinetics at alkaline pH 9,16,17, 19,20 . If caffeine is weakening the HBE, as indicated by the negative shift in the HUPD onset threshold on Pt(111) (Figure 1(b)), and the improved HER/HOR kinetics were a direct result of the weakened HBE, a similar result would be expected in acid.…”

“…It is likely that the thin caffeine film on the surface of Pt disrupts the double layer structure to directly affect the water orientation and dynamics. It has been proposed that at high pH, the stronger electric field at a given potential induces rigidity in the near surface water, lowering reorganization kinetics and impeding charge transfer 9, 19,20 . Caffeine at the metal/electrolyte interface may improve alkaline HER/HOR kinetics by weakening the electric field near reversible hydrogen potential, making water reorganization more facile.…”

Ionicity-dependent proton-coupled electron transfer of supramolecular self-assembled electroactive heterocycles

“…Indeed, given the large electrolyte concentrations adjacent to the electrode, we expect these effects may be even more prominent in the electrochemical double layer. 26,27 Previously in the analysis of self-association in PCET systems, varying concentration has been an entry into the analysis of the interactions. 18 (Fig.…”