Insight into the Transition‐Metal Hydroxide Cover Layer for Enhancing Photoelectrochemical Water Oxidation

Abstract

Depositing a transition‐metal hydroxide (TMH) layer on a photoanode has been demonstrated to enhance photoelectrochemical (PEC) water oxidation. However, the controversial understanding for the improvement origin remains a key challenge to unlock the PEC performance. Herein, by taking BiVO4/iron‐nickel hydroxide (BVO/FxN4−x‐H) as a prototype, we decoupled the PEC process into two processes including charge transfer and surface catalytic reaction. The kinetic information at the BVO/FxN4−x‐H and FxN4−x‐H/electrolyte interfaces was systematically evaluated by employing scanning photoelectrochemical microscopy (SPECM), intensity modulated photocurrent spectroscopy (IMPS) and oxygen evolution reaction (OER) model. It was found that FxN4−x‐H acts as a charge transporter rather than a sole electrocatalyst. PEC performance improvement is mainly ascribed to the efficient suppression of charge recombination by fast hole transfer kinetics at BVO/FxN4−x‐H interface.

Remarkable synergy of borate and interfacial hole transporter on BiVO4 photoanodes for photoelectrochemical water oxidation

“…Open Generally, loading an OEC catalyst on a photoanode should result in an increase in water oxidation rates. 16,20,43 However, k trans of bare BiVO 4 appeared higher than that of NiFeV/B-BiVO 4 to some degree at most potentials (Fig. 4d).…”

“…The photovoltage of a photoanode arises from splitting of electron and hole quasi-Fermi level under steady-state light illumination, which acts as a driving force for injecting the photogenerated holes into the electrolyte for OER. 65,67 According to several previous works, 30,43,49,62,68 the simple integration of OECs on the surface of photoanodes could enlarge the difference in photovoltage between the dark and light conditions, resulting in greater band bending. 44 Smith and co-workers also reported that the photocharged BiVO 4 photoanodes in a borate buffer solution obtained a favorable band bending, which is responsible for the strong suppression of surface recombination.…”

“…In this study, we solved this problem via integration of a NiFe-based LDH, an excellent electrocatalyst for oxygen evolution reaction (OER), [40][41][42] also recognized as hole transfer and storage layer for photoelectrodes. 30,[43][44][45] Under the synergetic effect of molecular borate and NiFeV co-modifications, the resulting NiFeV/B-BiVO 4 photoanode exhibited an outstanding photocurrent density of 4.6 mA cm -2 at 1.23 V RHE with an ultra-low onset potential of ~ 0.2 V RHE and superior photostability. NiFeV OECs served as not only a sole electrocatalyst for water oxidation but also a hole reservoir that efficiently suppressed surface charge recombination and accelerated interfacial charge transfer.…”

Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

“…Understanding the atomic nature of reactive sites and surface traps is a key enabling step towards optimizing chemical conversion at semiconductor-liquid junctions. [1][2][3] The recent development of operando analysis tools has provided deep insights into the operation of specific semiconductor electrodes for solar-driven H 2 production via water splitting. [4][5][6][7] However, each material brings a unique atomic and electronic structure that requires the development of specific analysis tools and interpretation.…”

Identifizierung von reaktiven Zentren und Oberflächenfallen in Chalkopyrit‐Photokathoden

“…Das Verständnis der atomaren Natur reaktiver Zentren und Oberflächenfallen ist ein wichtiger Schritt zur Optimierung der chemischen Umwandlung an Halbleiter-Flüssigkeit-Grenzflächen. [1][2][3] Die jüngste Entwicklung von Operando-Analysetools hat tiefe Einblicke in den Betrieb spezifischer Halbleiterelektroden für die solarbetriebene H 2 -Produktion durch Wasserspaltung ermçglicht. [4][5][6][7] Jedes Material bringt jedoch eine einzigartige atomare und elektronische Struktur mit sich, die die Entwicklung spezifischer Analysewerkzeuge und Interpretation erfordert.…”