Enhanced Stability and Activity for Water Oxidation in Alkaline Media with Bismuth Vanadate Photoelectrodes Modified with a Cobalt Oxide Catalytic Layer Produced by Atomic Layer Deposition

Abstract

Atomic-layer deposition (ALD) of thin layers of cobalt oxide on n-type BiVO4 produced photoanodes capable of water oxidation with essentially 100% faradaic efficiency in alkaline, pH = 13 electrolytes. By contrast, under the same operating conditions, BiVO4 photoanodes without the Co oxide catalytic layer exhibited lower faradaic yields, of ca. 70%, for O2 evolution and were unstable, becoming rapidly photopassivated. High numbers (>25) of ALD cycles of Co oxide deposition gave electrodes that displayed poor photoelectrochemical behavior, but 15–20 ALD cycles produced Co oxide overlayers ∼1 nm in thickness, with the resulting photoelectrodes exhibiting a stable photocurrent density of 1.49 mA cm–2 at the oxygen-evolution potential and an open-circuit potential of 0.404 V versus the reversible hydrogen electrode, under 100 mW cm–2 of simulated air mass 1.5 illumination.

Efficient Water‐Splitting Device Based on a Bismuth Vanadate Photoanode and Thin‐Film Silicon Solar Cells

“…[25] By taking this into account, the 4.22 mA cm À2 photocurrent density that we observe with the combination of BiVO 4 and micromorph Si corresponds to an apparent h STH of 5.2 %, which represents the current benchmark for standalone water-splitting devices based on a metal oxide photoelectrode. [9][10]26] Although the increase in h STH (4.9 [9] to 5.2 %) may seem incremental, the implication is very significant. Recent technoeconomic analyses have shown that efficiency is the most important knob in determining the resulting cost of hydrogen.…”

“…With a theoretical photocurrent density of 7.5 mA cm À2 for BiVO 4 , there is plenty of room for improvement by the combination of BiVO 4 and single-junction a-Si:H. In contrast, only little improvements are possible for the BiVO 4 /double-junction Si cell devices, in which the total photocurrent density is already close to the maximum photocurrent density of the double-junction Si cell. [9,10,17] A configuration with a single-junction a-Si:H cell therefore seems the most promising route for the further development of hybrid PEC/PV devices.…”

“…[1] For light-induced water splitting, transition-metal oxides, such as TiO 2 , [2,3] WO 3 , [4] Fe 2 O 3 , [5][6][7][8] and BiVO 4 , [9,10] have been widely used as photoanode materials. In particular, BiVO 4 is among the most promising photoanode materials for this application because of its direct energy gap of about 2.4 eV, its environmental friendliness, and its longterm stability in neutral and basic electrolytes.…”

Operando Analyses of Solar Fuels Light Absorbers and Catalysts

“…In addition to the overpotentials associated with the anode and cathode reactions and other system losses, the thermodynamic potential needed to split water, 1.23 V under standard conditions, imposes constraints on the operating photovoltage produced by the light absorber. Intensive efforts have focused on transition-metal oxides (TMOs) for watersplitting applications [4][5][6]. An alternative approach involves dual light absorbers, analogous to the Z-scheme of natural photosynthesis [7,8].…”

Stabilization of n-cadmium telluride photoanodes for water oxidation to O2(g) in aqueous alkaline electrolytes using amorphous TiO2 films formed by atomic-layer deposition

“…4a was predominantly associated with the faradaic oxidation of H 2 O to O 2. Direct verication of this hypothesis was obtained using an oxygen detector, 20 which revealed that n-CdTe/TiO 2 /Ni samples Oxygen production detected by a fluorescent probe and derived from coulometry during constant potential electrolysis at 1.23 V vs. RHE in pH ¼ 14 KOH(aq). In (a), the n-CdTe/TiO 2 /Ni electrode was illuminated by a Xenon arc lamp that had been calibrated to provide 100 mW cm À2 of simulated AM1.5G illumination; in (b), 20 mW cm À2 was used to prevent bubble formation.…”