A&P Seminar - Franz Geiger
Sep
16
2025
Description
The Analytical and Physical Seminar Series presents: Franz Geiger
Northwestern University
Host: Lauren Webb
Title: They flip before they split! New physical insights into the oxygen evolution reaction from nonlinear laser spectroscopy
Location: WEL 2.122
Refreshments served at 3:15pm
Water's oxygen is the electron source in the industrially important oxygen evolution reaction (OER) but how water interacts with an electrode surface remains enigmatic. While much microscopic insight into the Stern layer comes from atomistic simulations or joint theory-experiment approaches, water's strong absorber problem has clouded our view of how many water molecules change their alignment in response to applied potentials and what the associated energetics are. Here we employ nonlinear optical amplitude and phase measurements carried out with an ultrafast pulse triplet at metallic (nickel), semiconductor (hematite), and multi-element nanolayer electrodes under operando conditions of varying applied potentials. We identify a disorder-to-order transition in the Stern layer water molecules before the onset of Faradaic current that is closely recapitulated by a 2-dimensional Ising model. A full water monolayer (1.1 × 10^15 cm^−2) aligns with oxygen atoms pointing toward the electrode at +0.8 volt vs Ag/AgCl and the associated work is 80 kJ mol^-1. Our findings suggest a causal relationship between the need for Stern layer water flipping and the OER overpotential which may lead to developing strategies for decreasing the latter. Results from new experiments establishing our approach’s utility for photo-driven electrocatalysis are presented as well. Our experiments contribute to the growing field of molecular electrochemistry, provide benchmarks for electrical double layer models, and serve as a diagnostic tool for understanding electrocatalysis from a molecular perspective. This presentation is based on work published in Nature Communications (2025), Science Advances (2025), JACS (2025), and JPC A (2024).