# Recent Advances in Photoelectrochemical Nitrate Reduction to Ammonia

## TL;DR

This review discusses a green method for making ammonia using solar energy, which could replace the energy-intensive Haber-Bosch process.

## Contribution

The paper provides a systematic review of recent advances in designing efficient photocathodes for solar-driven nitrate-to-ammonia conversion.

## Key findings

- Efficient photocathodes can be designed using semiconductor materials and cocatalysts to enhance nitrate reduction.
- Bias-free PEC systems can produce ammonia and value-added chemicals simultaneously using integrated photoanodes and photocathodes.
- Mechanistic studies highlight the potential for scalable solar-driven ammonia synthesis.

## Abstract

Ammonia, as an essential chemical, plays an indispensable role in both industry and agriculture. However, the traditional Haber–Bosch technique for ammonia synthesis suffers from high energy consumption and significant CO2 emissions. Therefore, developing an energy-efficient and eco-friendly method for ammonia production is imperative. Photoelectrochemical (PEC) nitrate reduction to ammonia has emerged as a promising green alternative, which utilizes renewable solar energy to convert nitrate into valuable ammonia, thereby contributing to nitrogen recycling and wastewater remediation. This review systematically summarizes recent advances in PEC nitrate reduction to ammonia, focusing on the rational design of efficient photocathodes with the development of semiconductor materials, cocatalysts, p–n junction and heterostructure strategies. Furthermore, the integration of photocathodes with photoanodes enables the assembly of bias-free PEC systems capable of simultaneously producing ammonia and value-added chemicals, demonstrating the potential for scalable solar-driven ammonia synthesis. The mechanistic studies and future research directions are also discussed. The review aims to offer valuable insights and promote the further development of PEC nitrate reduction to ammonia.