Pt Single‐Atom Catalysts on FTO for Optically Invisible pH‐Universal Hydrogen Evolution Electrodes

Transparent hydrogen-evolution electrodes are essential for photoelectrochemical and optoelectronic energy-conversion devices, yet typically suffer from a trade-off between catalytic activity and optical transmission. Here, we demonstrate that an ultra-low loading of Pt single atoms (SA, 0.03 at%) directly anchored on fluorine-doped tin oxide (FTO) via a reactive deposition delivers hydrogen evolution reaction (HER) kinetics approaching bulk Pt, while remaining optically invisible. At this low SA loading, HAADF-STEM directly resolves atomically isolated Pt sites, while x-ray photoelectron and absorption spectroscopy confirm exclusively cationic Pt$^{δ+}$ (δ ≈ 2) in Pt–O$_4$ coordination. The Pt SA/FTO electrodes exhibit pH-universal HER activity, alongside turnover frequencies exceeding 500 s$^{−1}$ at moderate overpotentials. Density Functional Theory calculations support the high stability of Pt SA/FTO and explain exceptional HER activity by optimized energetics of intermediate formation. Achieving comparable kinetics with conventional sputtered Pt films requires >1000-fold higher Pt loading and leads to substantial optical losses. ... mehrOwing to its optical neutrality, the Pt SA/FTO electrode enables 2–3 × higher photocurrents than activity-matched Pt films when used as a counter electrode in sandwich-type photoelectrochemical cells. These results on Pt SA-decorated FTO thus describe a general strategy to unite noble-metal utilization, high catalytic efficiency, and optical transparency in electro- and photoelectrochemical devices.