Understanding the Stability of Etched or Platinized p-GaInP Photocathodes for Solar-Driven H₂ Evolution

Abstract

The long-term stability in acidic or alkaline aqueous electrolytes of p-Ga 0.52 In 0.48 P photocathodes, with a band gap of ∼1.8 eV, for the solardriven hydrogen-evolution reaction (HER) has been evaluated from a thermodynamic, kinetic, and mechanistic perspective. At either pH 0 or pH 14, etched p-GaInP electrodes corroded cathodically under illumination and formed metallic In 0 on the photoelectrode surface. In contrast, under the same conditions, electrodeposition of Pt facilitated the HER kinetics and stabilized p-GaInP/Pt photoelectrodes against such cathodic decomposition. When held at 0 V versus the reversible hydrogen electrode, p-GaInP/Pt electrodes in either pH = 0 or pH = 14 exhibited stable current densities (J) of ∼−9 mA cm −2 for hundreds of hours under simulated 1 sun illumination. During the stability tests, the current density−potential (J−E) characteristics of the p-GaInP/Pt photoelectrodes degraded due to pH-dependent changes in the surface chemistry of the photocathode. This work provides a fundamental understanding of the stability and corrosion mechanisms of p-GaInP photocathodes that constitute a promising top light absorber for tandem solar-fuel generators.

Failure Modes of Platinized pn+-GaInP Photocathodes for Solar-Driven H2 Evolution

“…The two pn + -GaInP/Pt photoelectrodes exhibited similar leaching rates of In ions of 0.73 and 0.64 nm h –1 during the first 100 h of CA at 0.5 or 0 V vs RHE, respectively (Figure e,f). These linear dissolution rates were comparable to values observed in our previous study of p-GaInP at pH = 0 . The slight increase in | J ph | after 41 h seen in Figure c is consistent with a decrease in parasitic light absorption resulting from partial dissolution of the n + -GaInP emitter at the front surface of the electrode …”

“…In contrast, etched p-GaAs exhibits neither appreciable cathodic corrosion nor electrode dissolution even under potentials, E , as negative as −0.6 V vs RHE. , However, electrodeposition of Pt on a p-GaAs surface results under HER conditions in the formation of an As 0 -rich surface, which further damages the photoactivity of the electrode . Similarly, the cathodic corrosion of p-Ga 0.52 In 0.48 P photocathodes is initiated by the In 3+ cations and is controlled by the surface kinetics . Collectively, these findings suggest that the Ga–In–P combination should constitute the most promising candidate for a large band gap (1.8 eV) III–V alloy light-absorber in a tandem solar fuel device as surface As 0 may be harmful to the photoactivity, whereas the cathodic corrosion of In 3+ cations can be inhibited in acidic media by HER catalysts.…”

“…Recently, we performed a series of investigations on the stability of III–V semiconductor photocathodes under HER conditions. − By combining experimental results with the predictions of the Pourbaix diagram, generalizable factors that govern the stability of these semiconductors as photocathodes, including catalytic kinetics and surface stoichiometry, were identified. ,, Specifically for InP, the In 3+ cations are susceptible to cathodic corrosion to form metallic In 0 , but in acidic media, this process can be mitigated via kinetic control by an electrodeposited Pt catalyst. In KOH­(aq), the surface of p-InP/Pt photocathodes undergoes passivation by InO x , resulting in a degradation in the J – E behavior .…”

“…Prior to long-term tests, a Pt catalyst was galvanostatically electrodeposited onto the GaInP surface to obtain integrated pn + -GaInP/Pt photocathodes. The Pt catalyst facilitated the HER kinetics and resulted in a low overpotential at photoelectrode surface to effect | J | > 10 mA cm –2 , thus suppressing the cathodic corrosion of In 3+ cations. , During chronoamperometry (CA) at various applied potentials E , the long-term evolution of the J – E behavior of pn + -GaInP/Pt photocathodes was correlated with the electrode dissolution examined by inductively coupled plasma mass spectrometry (ICP-MS) and the surface characteristics indicated by X-ray photoelectron spectroscopy (XPS).…”

Advances in Engineered Metal Oxide Thin Films by Low-Cost, Solution-Based Techniques for Green Hydrogen Production

“…Similarly, GaP and Ta 3 N 5 suffer photocorrosion and surface oxidation in alkaline media, resulting in poor stability toward the water splitting reaction, which limits their application to only a few minutes without any protective surface layer [26][27][28][29]. Other semiconductors, such as III-V photoanodes [30][31][32][33][34] or a doped BiVO 4 scheelite structure [35][36][37], have shown interesting results. Still, their fabrication costs, photocorrosion, and instability issues in aqueous solution make them unsuitable for water splitting.…”