Stable hybrid organic/inorganic photocathodes for hydrogen evolution with amorphous WO₃ hole selective contacts

Abstract

Photoelectrochemical H production through hybrid organic/inorganic interfaces exploits the capability of polymeric absorbers to drive photo-induced electron transfer to an electrocatalyst in a water environment. Photoelectrode architectures based on solution-processed organic semiconductors are now emerging as low-cost alternatives to crystalline inorganic semiconductors based on Si, oxides and III-V alloys. In this work, we demonstrate that the stability of a hybrid organic/inorganic photocathode, employing a P3HT:PCBM blend as photoactive material, can be considerably improved by introducing an electrochemically stable WO hole selective layer, paired with a TiO electron selective layer. This hybrid photoelectrode exhibits a photocurrent of 2.48 mA cm at 0 V, +0.56 V onset potential and a state-of the art operational activity of more than 10 hours. This work gives the perspective that photoelectrodes based on organic semiconductors, coupled with proper inorganic selective contacts, represent a sound new option for the efficient and durable photoelectrochemical conversion of solar energy into fuels.

Graphene-Based Hole-Selective Layers for High-Efficiency, Solution-Processed, Large-Area, Flexible, Hydrogen-Evolving Organic Photocathodes

“…179,180 The delamination/disruption is instead not observed in our HSL-free photocathodes, in agreement with previous studies. [75][76][77][78][79][80][81][82][83][84][85] Stabilizing strategies The decrease of the photocurrents observed during the potentiostatic stability test pointed out the need to implement stabilizing strategies to improve the endurance of the as-prepared photoelectrodes. Both Pt detachment/dissolution and delamination/disruption of the layered structure of the photocathodes based on GO and RGO can be at the origin of the performances degradation.…”

“…[75][76][77][78][79]84,85 The photocathode figures of merit (FoM) strongly depends on the presence of the HSL and ESL materials. 104 While TiO 2 and its sub-stoichiometric phases have demonstrated to be consolidated ESL materials, [80][81][82][83]85 the choice for the HSL counterpart has been a more complex task. In fact, although efficient HSL materials have been identified (e.g., MoO 3 , 77 WO 3 , 82 NiO, 80 CuI, 83,85 PEDOT:PSS [75][76][77][78][79][80][81] ) their intrinsic electrochemical degradation under HER-working conditions limited the lifetime of the photocathodes, lasting from several minutes to about few hours (up to 10 hours in the case of WO 3 ).…”

“…The optimization of the proposed architectures allowed us to achieve a recordhigh efficiency for solution-processed rr-P3HT:PCBM-based photocathodes, extending their operational activity up to 20 h. This result outperforms the state-of-the-art endurance for rr-P3HT:PCBM-based photocathodes (10 hours for photocathodes based on 100nm-thick WO 3 film as HSL). 82 Moreover, our photocathodes are extremely versatile, showing high PEC activity in different pH conditions, i.e., ranging from acid to basic. This is pivotal for the exploitation of the proposed photocathodes in tandem configurations, whose photoanode activity is usually facilitated in alkaline condition.…”

Carbon‐Based Photocathode Materials for Solar Hydrogen Production

“…[146] The stability of the WO3-based photocathodes was evaluated at 0.2 V vs. RHE, corresponding to the Vmpp for the device (Figure 9a). [58] Interestingly, the photocathodes continuously operated for more than 10 h, retaining 70% of their initial photocurrent densities after 8 h, surpassing the durability of previously developed P3HT:PCBM-based photocathodes. [52,53,54,55,56,57] However, the issue of degradation was not completely eliminated, most probably due to the proton intercalation within WO3, a process previously observed in MoO3 HSLs.…”

“…[61,62,64,66,[68][69][70]90] In addition, the CSLs raise the HER-operating potential window of architecture (2) to values that are more positive vs. RHE. [58,61,62,64,66,[68][69][70]90] Notably, the simultaneous use of an EC and CSLs improves the PEC stability of the light absorber, avoiding photoelectrochemical degradation (e.g., self-photocorrosive reactions). [107] Based on this consideration, the PEC behaviour of the different architectures is graphically sketched in Figure 2b.…”