Investigations of the stability of etched or platinized p-InP(100) photocathodes for solar-driven hydrogen evolution in acidic or alkaline aqueous electrolytes

• Published in: Energy & environmental science Vol. 14; no. 11; pp. 67 - 62
• Main Authors: Yu, Weilai, Richter, Matthias H, Buabthong, Pakpoom, Moreno-Hernandez, Ivan A, Read, Carlos G, Simonoff, Ethan, Brunschwig, Bruce S, Lewis, Nathan S
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 10.11.2021; Royal Society of Chemistry (RSC)
• Subjects: Aqueous electrolytes; Catalysts; Cathodic corrosion; Coated electrodes; Corrosion; Corrosion mechanisms; Current density; Dissolution; Electrochemistry; Electrodes; Evaluation; Hydrogen; Hydrogen evolution reactions; Illumination; Inductively coupled plasma mass spectrometry; Leaching; Mass spectrometry; Mass spectroscopy; pH effects; Photocathodes; Photoelectron spectroscopy; Photoelectrons; Reaction kinetics; Stability analysis; Stoichiometry; Sulfuric acid; Surface chemistry; Surface properties; X ray photoelectron spectroscopy
• ISSN: 1754-5692; 1754-5706
• DOI: 10.1039/d1ee02809j

The stability of p-InP photocathodes performing the hydrogen-evolution reaction (HER) has been evaluated in contact with either 1.0 M H 2 SO 4 (aq) or 1.0 M KOH(aq), with a focus on identifying corrosion mechanisms. Stability for the solar-driven HER was evaluated using p-InP electrodes that were either etched or coated with an electrodeposited Pt catalyst (p-InP/Pt). Variables such as trace O 2 were systematically controlled during the measurements. Changes in surface characteristics after exposure to electrochemical conditions as well as electrode dissolution processes were monitored using X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). In either H 2 SO 4 or KOH, etched p-InP photoelectrodes corroded cathodically under illumination, forming metallic In 0 at the electrode surface. In contrast, electrodeposition of Pt kinetically stabilized illuminated p-InP photocathodes in both H 2 SO 4 and KOH by inhibiting the cathodic corrosion pathway. Notably, when held at 0 V vs. the reversible hydrogen electrode (RHE) in 1.0 M H 2 SO 4 (aq), p-InP/Pt exhibited a stable current density ( J ) of ∼−18 mA cm −2 for >285 h under simulated 1 Sun illumination. The long-term current density vs. potential ( J - E ) behavior at pH 0 and pH 14 of p-InP/Pt photocathodes correlated with changes in the surface chemistry as well as the dissolution of p-InP. In acidic media, the J - E behavior of p-InP/Pt photocathodes remained nearly constant with time, but the surface of a p-InP/Pt electrodes gradually turned P-rich via a slow and continuous leaching of In ions. In alkaline electrolyte, the surface of p-InP/Pt electrodes was passivated by formation of an InO x layer that exhibited negligible dissolution but led to a substantial degradation in the J - E characteristics. Consequently, changes in the catalytic kinetics and surface stoichiometry are both important considerations for determining the corrosion chemistry and the long-term operational stability of InP photoelectrodes. Illuminated etched p-InP photocathode undergoes cathodic corrosion forming metallic In 0 , while electrodeposited Pt catalyst kinetically stabilizes the electrode surface against such a corrosion pathway.