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

## TL;DR

A new hematite photoanode design boosts hydrogen production efficiency by using hydrazine oxidation instead of traditional methods.

## Contribution

Introduces a Ti-doped, hierarchically porous hematite photoanode with a record solar-to-hydrogen efficiency of 8.7%.

## Key findings

- The tp-Fe2O3 photoanode achieves a photocurrent density of 3.1 mA cm−2 at 1.23 V vs. RHE with exceptional stability.
- Hydrazine oxidation increases photocurrent to 7.1 mA cm−2 at 1.23 VRHE.
- Integration with a Si solar cell achieves a solar-to-hydrogen efficiency of 8.7%.

## Abstract

A multi-cycle growth and flame annealing strategy was developed to construct textured and hierarchically porous Ti-doped hematite (tp-Fe2O3) photoanodes with enhanced charge transport and surface kinetics.The hydrazine oxidation reaction was introduced as a fast and thermodynamically favorable alternative to the oxygen evolution reaction, enabling the simultaneous production of hydrogen and the remediation of toxic hydrazine.The tp-Fe2O3-based bias-free photovoltaic-photoelectrochemical tandem device achieved a record solar-to-hydrogen efficiency of 8.7%, demonstrating excellent stability and scalability for sustainable solar fuel generation.

A multi-cycle growth and flame annealing strategy was developed to construct textured and hierarchically porous Ti-doped hematite (tp-Fe2O3) photoanodes with enhanced charge transport and surface kinetics.

The hydrazine oxidation reaction was introduced as a fast and thermodynamically favorable alternative to the oxygen evolution reaction, enabling the simultaneous production of hydrogen and the remediation of toxic hydrazine.

The tp-Fe2O3-based bias-free photovoltaic-photoelectrochemical tandem device achieved a record solar-to-hydrogen efficiency of 8.7%, demonstrating excellent stability and scalability for sustainable solar fuel generation.

The online version contains supplementary material available at 10.1007/s40820-025-02045-z.

The performance of hematite (α-Fe2O3) 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 Fe2O3 (tp-Fe2O3) 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 Fe2O3 (nr-Fe2O3). As a result, the tp-Fe2O3 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 VRHE. Finally, when we integrate the tp-Fe2O3 with a commercial Si solar cell, it achieves a solar-to-hydrogen efficiency of 8.7%—the highest reported value for any Fe2O3-based PV-tandem system. This work provides critical insights into rational Fe2O3 photoanode design and highlights the potential of hydrazine as an efficient alternative anodic reaction, enabling waste valorization.

The online version contains supplementary material available at 10.1007/s40820-025-02045-z.