Tin Oxide as a Protective Heterojunction with Silicon for Efficient Photoelectrochemical Water Oxidation in Strongly Acidic or Alkaline Electrolytes

Abstract

Photoelectrodes without a p–n junction are often limited in efficiency by charge recombination at semiconductor surfaces and slow charge transfer to electrocatalysts. This study reports that tin oxide (SnOx) layers applied to n‐Si wafers after forming a thin chemically oxidized SiOx layer can passivate the Si surface while producing ≈620 mV photovoltage under 100 mW cm−2 of simulated sunlight. The SnOx layer makes ohmic contacts to Ni, Ir, or Pt films that act as precatalysts for the oxygen‐evolution reaction (OER) in 1.0 m KOH(aq) or 1.0 m H2SO4(aq). Ideal regenerative solar‐to‐O2(g) efficiencies of 4.1% and 3.7%, respectively, are obtained in 1.0 m KOH(aq) with Ni or in 1.0 m H2SO4(aq) with Pt/IrOx layers as OER catalysts. Stable photocurrents for >100 h are obtained for electrodes with patterned catalyst layers in both 1.0 m KOH(aq) and 1.0 m H2SO4(aq).

Water oxidation with inhomogeneous metal-silicon interfaces

“…[41] A recent very interesting report demonstrates that thick (~100 nm) layers of spray-deposited SnO x on n-Si produces a high barrier heterojunction that can be employed for promoting OER with a photovoltage of ~620 mV for 100 h when interfaced with highly-active OER cocats. [42] 2-2-Combining protection and activity in a single layer An alternative and highly beneficial strategy that has also been employed to decrease the manufacturing costs consists in employing a coating material that acts as a Si protection layer and, as the same time, as a cocat. We refer here to this configuration as Si/co-catalytic protection layer (Si/pc).…”

“…[79] Such a stability could first seem unexpected considering such corrosive environments for Si, and that the largest Si part is covered by nothing but its anodic oxide. If these unexpected recent reports are exciting, the performance of inhomogeneous photoanodes manufactured this way is still far from their conformal, oxide-coated, counterparts in terms of photovoltage [42] but also stability. [26] Nevertheless, it is expected that considerable progress could be obtained through a better understanding of the pinch-off effect as well as a fine characterization of the Si/metal, Si/SiO x and SiO x /metal interfaces, that all seem to play an important role for photovoltage generation and stability.…”

Interface engineering of Ta3N5 thin film photoanode for highly efficient photoelectrochemical water splitting

“…Over the past decade, tremendous efforts have been devoted to interface engineering of various semiconductor photoelectrodes (e.g., Si 20,21 , α-Fe 2 O 3 22 , BiVO 4 23 , Cu 2 O 24 ) to improve their efficiency and stability through the passivation of interfacial defects or formation of hetero-/homojunctions. Ideally, the semiconductor thin film light absorbers should be sandwiched by a n-type electron transport layer (ETL) and a p-type hole transport layer (HTL) to achieve efficient charge separation, similar to the "n-i-p" device architecture commonly used in thin-film photovoltaics 25 .…”

A Review of Inorganic Photoelectrode Developments and Reactor Scale‐Up Challenges for Solar Hydrogen Production

“…developed n‐Si wafers for use as photoanodes. [ 166 ] The wafers were passivated with a layer of SnO x , grown by spray pyrolysis, and then coated with a Ni surface co‐catalyst using a physical vapor deposition method. The photoanodes showed onset potentials of ≈0.9 V RHE and photocurrent densities of ≈31 mA cm −2 , with a η STH of 4.1%.…”