Fundamental Limitations of Cu(II)-based Oxides for Photoelectrochemical Nitrogen Reduction
9 affiliations
- 1Walter Schottky Institute
- 2Technical University of Munich
- 3Physics Department, TUM School of Natural Sciences
- 4Institute of Electrochemistry
- 5Ulm University
- 6Max Planck Institute for Sustainable Materials
- 7Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
- 8Helmholtz Institute Ulm for Electrochemical Energy Storage
- 9Karlsruhe Institute of Technology
Abstract
The photoelectrochemical (PEC) nitrogen reduction reaction (N 2 RR) offers a potentially sustainable route to ammonia (NH 3 ) synthesis. However, reliable evaluation of PEC N 2 RR activity remains challenging due to contamination-induced false positives and competing reactions. Here, we comparatively investigate p -type CuBi 2 O 4 and the previously reported PEC N 2 RR-active photocathode CuO, using an ultra-clean, contamination-controlled measurement system. Despite favorable band energetics and measurable photocurrents, neither material exhibits statistically significant NH 3 production, suggesting that the previously reported activity of CuO most likely originated from contamination-induced false positives rather than genuine N 2 reduction. Density functional theory further shows that the first proton-coupled electron transfer step toward *NNH formation remains kinetically prohibitive, even on oxygen-deficient surfaces, strongly favoring the competing hydrogen evolution reaction (HER). In addition, both photocathodes undergo surface reduction and photocorrosion. Nevertheless, comparative analysis reveals fundamentally different degradation pathways on the two photocathodes. While CuBi 2 O 4 retains its bulk structural integrity under photocathodic conditions, CuO undergoes extensive reduction, restructuring, and dissolution. Together, these findings highlight the importance of contamination control in evaluating aqueous PEC N 2 RR, as well as the challenges of overcoming vigorous competition with HER and photocorrosion processes using Cu(II)-based oxides.
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BibTeX
@misc{christis2026fundamental,
title = {{Fundamental Limitations of Cu(II)-based Oxides for Photoelectrochemical Nitrogen Reduction}},
author = {Maximilian Christis and Saswati Santra and Julian Beßner and Yiqun Jiang and Xiang Li and Jasmin Zitzmann and Andrea M. Mingers and Stefanie Bogenrieder and Björn Kirchhoff and Verena Streibel and Siyuan Zhang and Timo Jacob and Ian D. Sharp},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010116/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010116/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Fundamental Limitations of Cu(II)-based Oxides for Photoelectrochemical Nitrogen Reduction
AU - Maximilian Christis
AU - Saswati Santra
AU - Julian Beßner
AU - Yiqun Jiang
AU - Xiang Li
AU - Jasmin Zitzmann
AU - Andrea M. Mingers
AU - Stefanie Bogenrieder
AU - Björn Kirchhoff
AU - Verena Streibel
AU - Siyuan Zhang
AU - Timo Jacob
AU - Ian D. Sharp
PY - 2026
DA - 2026/10/08
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010116/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010116/v1
AB - The photoelectrochemical (PEC) nitrogen reduction reaction (N 2 RR) offers a potentially sustainable route to ammonia (NH 3 ) synthesis. However, reliable evaluation of PEC N 2 RR activity remains challenging due to contamination-induced false positives and competing reactions. Here, we comparatively investigate p -type CuBi 2 O 4 and the previously reported PEC N 2 RR-active photocathode CuO, using an ultra-clean, contamination-controlled measurement system. Despite favorable band energetics and measurable photocurrents, neither material exhibits statistically significant NH 3 production, suggesting that the previously reported activity of CuO most likely originated from contamination-induced false positives rather than genuine N 2 reduction. Density functional theory further shows that the first proton-coupled electron transfer step toward *NNH formation remains kinetically prohibitive, even on oxygen-deficient surfaces, strongly favoring the competing hydrogen evolution reaction (HER). In addition, both photocathodes undergo surface reduction and photocorrosion. Nevertheless, comparative analysis reveals fundamentally different degradation pathways on the two photocathodes. While CuBi 2 O 4 retains its bulk structural integrity under photocathodic conditions, CuO undergoes extensive reduction, restructuring, and dissolution. Together, these findings highlight the importance of contamination control in evaluating aqueous PEC N 2 RR, as well as the challenges of overcoming vigorous competition with HER and photocorrosion processes using Cu(II)-based oxides.
ER -