Boosting the performance of Cu2O photocathodes for unassisted solar water splitting devices

Abstract

Although large research efforts have been devoted to photoelectrochemical (PEC) water splitting in the past several decades, the lack of efficient, stable and Earth-abundant photoelectrodes remains a bottleneck for practical application. Here, we report a photocathode with a coaxial nanowire structure implementing a Cu 2 O/Ga 2 O 3-buried p-n junction that achieves efficient light harvesting across the whole visible region to over 600 nm, reaching an external quantum yield for hydrogen generation close to 80%. With a photocurrent onset over + 1 V against the reversible hydrogen electrode and a photocurrent density of ~10 mA cm −2 at 0 V versus the reversible hydrogen electrode, our electrode constitutes the best oxide photocathode for catalytic generation of hydrogen from sunlight known today. Conformal coating via atomic-layer deposition of a TiO 2 protection layer enables stable operation exceeding 100 h. Using NiMo as the hydrogen evolution catalyst, an all Earth-abundant Cu 2 O photocathode was achieved with stable operation in a weak alkaline electrolyte. To show the practical impact of this photocathode, we constructed an all-oxide unassisted solar water splitting tandem device using state-of-the-art BiVO 4 as the photoanode, achieving ~3% solar-to-hydrogen conversion efficiency.

Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO2‐Protected Sb2Se3 Photocathodes for Photo‐Electrochemical Water Splitting

“…After a simple interface modification made by introducing a C 60 photoelectron transfer promoter, the PEC stability was exceptionally improved more than fivefold, hinting at the promising versatility of C 60 and it being applicable to various photoelectrodes. Although the stability can be measured at a potential more positive than 0 V RHE , particularly in the case of a tandem device to show stability at the operation point, [12] most of the photocathodes studies show the stability at 0 V RHE ; thus we report the stability at 0 V RHE here. Although the stability can be measured at a potential more positive than 0 V RHE , particularly in the case of a tandem device to show stability at the operation point, [12] most of the photocathodes studies show the stability at 0 V RHE ; thus we report the stability at 0 V RHE here.…”

Recent Advances and Emerging Trends in Photo‐Electrochemical Solar Energy Conversion

“…[23,24] The following year Seger et al reported a stabilized silicon-based photocathode with earthabundant MoS x hydrogen evolution catalyst using a thin Ti metal film as a protection layer. [26][27][28][29][30][31][32][33] Emerging materials such as Sb 2 Se 3 , [34,35] Cu 2 ZnSnS 4 (CZTS), [36][37][38] CuO, [39] CuInxGa (1-x) Se 2 (CIGS), [40] and CuBi 2 O 4 [41,42] have also been investigated with protective overlayers. [26][27][28][29][30][31][32][33] Emerging materials such as Sb 2 Se 3 , [34,35] Cu 2 ZnSnS 4 (CZTS), [36][37][38] CuO, [39] CuInxGa (1-x) Se 2 (CIGS), [40] and CuBi 2 O 4 [41,42] have also been investigated with protective overlayers.…”

Directly Photoexcited Oxides for Photoelectrochemical Water Splitting

“…[88] These features render Cu 2 Oo ne of the most promising semiconductors for PEC water splitting. Earth-abundant catalysts, such as NiMo, [91,92] MoS 2 , [93] and FeNiO x , [94] were also appliedo nC u 2 Op -PEs to lower the cost. [89] Seminal work was performed by Paracchino et al,w ho depositeda luminum-doped zinc oxide (AZO) and titaniumo xide (TiO 2 )t hrough atomic layer deposition (ALD), as shown in Figure 4a.…”

“…The two main factorsf or Cu 2 Od egradationw ere greatly alleviated, resulting in a j ph of 7.6 mA cm À2 at 0V versus RHE under AM 1.5G simulated sunlight. [92,96,98] The electrons only have to travel alongt he radius of the wire. Later work on improving the stabilityo ft he system replaced the Pt catalysta nd modifiedt he TiO 2 layer.R uO x was used as a substitute of Pt to improvet he kinetics of the hydrogen evolution reaction.…”