Bias-Free Photoelectrochemical Nitrobenzene-to-Aniline Conversion via a Bidirectional Hydrogen Balance System

Developing a low-cost and pollution-free Haber-type process has importance for the modern chemical industry, which traditionally relies on stoichiometric reductants under harsh conditions, generating significant waste and posing safety risks. Photoelectrochemical (PEC) hydrogenation offers a promising alternative using water and solar energy. However, its implementation for six-electron/six-proton reduction, such as nitrobenzene to aniline (NB-to-AN), faces two major hurdles: severe charge carrier recombination and inefficient hydrogen provision. To overcome these problems, we propose a “bidirectional hydrogen balance system” integrating a Cu-deficient CuBi2O4 (Cu1–xBi2O4) photocathode (enhancing charge separation via Cu vacancies) with a BiVO4 photoanode performing hydrazine oxidation reaction (HzOR). The HzOR simultaneously lowers the system energy demand and supplies protons for cathodic reduction. The tandem device achieved a photocurrent density of 1.23 mA/cm2 without external bias under 1 sun illumination, retained 88.6% activity after 15 h, and delivered near-quantitative NB conversion and AN selectivity (∼100%), demonstrating a pollution-free, efficient PEC approach for Haber-type processes.