Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode

Abstract

Metal oxides are generally very stable in aqueous solutions and cheap, but their photochemical activity is usually limited by poor charge carrier separation. Here we show that this problem can be solved by introducing a gradient dopant concentration in the metal oxide film, thereby creating a distributed n þ -n homojunction. This concept is demonstrated with a lowcost, spray-deposited and non-porous tungsten-doped bismuth vanadate photoanode in which carrier-separation efficiencies of up to 80% are achieved. By combining this state-ofthe-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double-or single-junction amorphous Si solar cell in a tandem configuration, stable shortcircuit water-splitting photocurrents of B4 and 3 mA cm À 2 , respectively, are achieved under 1 sun illumination. The 4 mA cm À 2 photocurrent corresponds to a solar-to-hydrogen efficiency of 4.9%, which is the highest efficiency yet reported for a stand-alone water-splitting device based on a metal oxide photoanode.

Efficient Water Splitting Cascade Photoanodes with Ligand‐Engineered MnO Cocatalysts

“…The BF 4 ‐treated MnO/BiVO 4 /WO 3 anode achieved 6.25 mA cm −2 at the 1.23 V versus RHE. We emphasize that the photocurrent of BF 4 ‐treated MnO attached to the BiVO 4 /WO 3 anode is the highest of the previously reported BiVO 4 ‐based photoanodes with hole scavenger for solar water splitting, as shown in Table S2 and Figure S4 (Supporting Information) 13, 14, 16, 17, 21, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69. Otherwise, Ca–EDTA‐treated MnO NPs/BiVO 4 /WO 3 recorded the lowest photocurrent density of about 2.5 mA cm −2 .…”

“…Therefore, most of the previously reported results related to BiVO 4 ‐based photoanodes13, 14, 16, 19, 47, 51, 52, 53 were measured in sulfite oxidation condition to show photo‐electrochemical properties of BiVO 4 ‐based electrodes independently of its poor water oxidation kinetics, as shown in Table S2 (Supporting Information). The photo‐electrochemical current densities of the BiVO 4 ‐based photoanodes4, 13, 14, 16, 17, 19, 20, 21, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 77 were plotted as a function of potential versus RHE. Thus, we measured PEC properties of BiVO 4 ‐based anodes under sulfite oxidation to figure out the effect of ligand engineering.…”

Recent Progress in Energy‐Driven Water Splitting

“…Other recent advances also include solar water‐splitting device based on the combination of W‐doped BiVO 4 photoanode and a two‐junction silicon solar cell with a ≈4.9% solar‐to‐hydrogen efficiency 192. The most notable work on “artificial leaf” involved the use of a triple junction and amorphous silicon photovoltaic interfaced to hydrogen‐ and oxygen‐evolving catalyst for yielding 4.7% efficiency 193.…”

“…Research efforts have recently focussed on the development of promising transition metal oxides such as TiO 2 , WO 3 , Fe 2 O 3 and BiVO 4 as photoelectrode in tandem water splitting device 192, 195. The envisioned strategy is to develop PEC tandem configurations based on a front visible light‐absorbing metal oxide photoelectrode combined with a rear small band gap solar cell.…”

Direct Solar Charging of an Organic–Inorganic, Stable, and Aqueous Alkaline Redox Flow Battery with a Hematite Photoanode

“…However, the current work is a proof‐of‐principle of a solar charged RFB that is stable, non‐toxic, non‐flammable, and uses low cost and environmentally benign materials. Future investigations in new redox pairs, use of other low‐cost phototoelectrodes such as Cu 2 O or BiVO 4 or tandem photoelectrode systems, which have been widely described, may lead to higher efficiencies and feasible solar charged redox flow batteries 19. For surface treatments, other conducting polymers such as polyacetylene and polyphenylene could be tested with other photoelectrodes in other electrolyte systems.…”