Textured and Hierarchically Porous Hematite Photoanode for Efficient Hydrogen Production via Photoelectrochemical Hydrazine Oxidation

This is the authors' abstract. We don't add key points for this paper.

The performance of hematite (α-Fe 2 O 3 ) photoanodes for photoelectrochemical (PEC) water splitting has been limited to around 2–5 mA cm −2 under standard conditions due to their short hole diffusion length and sluggish oxygen evolution reaction kinetics. This work overcomes those challenges through a synergistic strategy that co-designs the hematite architecture and the surface reaction pathway. We introduce a textured and hierarchically porous Ti-doped Fe 2 O 3 (tp-Fe 2 O 3 ) photoanode, synthesized via multi-cycle growth and flame annealing method. This unique architecture features a high texture (110), enlarged surface area, and hierarchically porous structure, which enable significantly enhanced bulk charge transport and interfacial charge transfer compared to typical nanorod Ti-doped Fe 2 O 3 (nr-Fe 2 O 3 ). As a result, the tp-Fe 2 O 3 photoanode achieves a photocurrent density of 3.1 mA cm −2 at 1.23 V vs. RHE with exceptional stability over 105 h, notably without any co-catalyst. By replacing the OER with the hydrazine oxidation reaction, the photocurrent further reaches a record-high level of 7.1 mA cm −2 at 1.23 V RHE . Finally, when we integrate the tp-Fe 2 O 3 with a commercial Si solar cell, it achieves a solar-to-hydrogen efficiency of 8.7%—the highest reported value for any Fe 2 O 3 -based PV-tandem system. This work provides critical insights into rational Fe 2 O 3 photoanode design and highlights the potential of hydrazine as an efficient alternative anodic reaction, enabling waste valorization.