Due to its essential use as a fertilizer, ammonia synthesis from nitrogen and hydrogen is considered to be one of the most important chemical processes of the last 100 years. Since then, an enormous amount of work has been undertaken to investigate and develop effective catalysts for this process. Although the catalytic synthesis of ammonia has been extensively studied in the last century, many new catalysts are still currently being developed to reduce the operating temperature and pressure of the process and to improve the conversion of reactants to ammonia. New catalysts for the Haber–Bosch process are the key to achieving green ammonia production in the foreseeable future. Herein, the history of ammonia synthesis catalyst development is briefly described as well as recent progress in catalyst development with the aim of building an overview of the current state of ammonia synthesis catalysts for the Haber–Bosch process. The new emerging ammonia synthesis catalysts, including electride, hydride, amide, perovskite oxide hydride/oxynitride hydride, nitride, and oxide promoted metals such as Fe, Co, and Ni, are promising alternatives to the conventional fused‐Fe and promoted‐Ru catalysts for existing ammonia synthesis plants and future distributed green ammonia synthesis based on the Haber–Bosch process.

This review features a thorough overview of direct ammonia fuel cells with focus on the effects of electrolyte, electrocatalyst and operating temperature. Remaining challenges and potential applications for this technology are highlighted.

For the first time, a working direct urea and direct urine fuel cell has been developed to generate electricity directly from urea or urine.