Publication date: 22nd July 2026
Photoelectrochemical (PEC) water splitting is a direct route to solar H2, but scaling to cm² areas is limited by ohmic drops, current collection and photoelectrode durability. We report a 10 cm² zero-gap tandem PEC cell built only from earth-abundant oxides (α-Fe2O3 photoanode/CuO photocathode) and an anion-exchange membrane. The work quantifies module-scale losses via EIS and distribution-of-relaxation-times analysis and assesses 240 h stability and gas purity.
Nanostructured α-Fe2O3 was electrodeposited on FTO and annealed; Cu was electrodeposited on carbon paper, chemically oxidised to Cu(OH)2 and converted to CuO. A PiperION AEM (OH− form) and matching ionomer layers formed a glass electrode membrane assembly in a PMMA/steel zero-gap prototype (10 cm²). J–V curves, EIS+DRT, 240 h potentiostatic test (−1.3 V) and Micro-GC were performed under AM 1.5G.
Under AM 1.5G the tandem delivers a photoresponse already near 0 V and reaches −25 mA cm−2 at −1.3 V, giving a maximum hydrogen-production efficiency of 5.1%. EIS shows an area-specific ohmic resistance of ~18 Ω cm², while illumination lowers the interfacial polarization (Rct ~32 Ω cm² at −1.3 V). DRT resolves a dominant millisecond relaxation assigned to charge transfer/double-layer dynamics, with slower contributions emerging at 0 V, consistent with transport/ionic redistribution in the membrane–electrode assembly. A 240-h durability test at −1.3 V maintains nearly constant current; Micro-GC confirms ~99.95% H2 with O2 at 0.04–0.06% and no detectable CO/CO2. Post-operando XRD/SEM show stable hematite, whereas CuO partially reduces and delaminates, identifying the photocathode and series resistance as the main scaling bottlenecks.
A bias-assisted 10 cm² α-Fe2O3/CuO tandem PEC cell in zero-gap AEM architecture achieves −25 mA cm−2 and 5.1% H2 efficiency at −1.3 V with 99.95% H2 purity over 240 h. Performance is governed by ~18 Ω cm² ohmic loss and CuO instability: future work will focus on reducing ohmic losses and on implementing protected photocathodes [1].
This work was supported by the Italian Ministry of the Environment and Energy Security (MASE) through the “Piano Triennale di Realizzazione 2022–2024 della Ricerca di Sistema Elettrico Nazionale – Progetto Integrato Tecnologie dell’Idrogeno” (Unique Project Code B53C22008610001) and the “Piano Triennale di Realizzazione 2025–2027 della Ricerca di Sistema Elettrico Nazionale – Project 1.3 ‘Tecnologie e usi finali dell’idrogeno’” (Unique Project Code B53C24009970001).
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