Recent progress in electrochemical synthesis of carbon-free hydrogen carrier ammonia and ammonia fuel cells: A review

Abstract

Ammonia (NH₃) is a cornerstone widely used in the modern agriculture and industry, the annual global production gradually increases to almost 200 million tons. Nearly 80% of the produced NH₃ is used in the fertilizer industry and is essential for the development of global agriculture and consequently for maintaining population growth. Furthermore, NH₃ can power hydrogen (H₂) fueled devices, such as H₂ fuel cells (FC), to use the interconversion between chemical energy and electric energy of nitrogen (N₂) cycle, which can effectively alleviate the intermittent problems of renewable energy. However, the problems faced by NH₃ in storage and release still restrict its development. Herein, this review introduces the latest research and development of electrochemical NH₃ synthesis and direct NH₃ FC, as well as outlines the technical challenges, possible improvement measures and development perspectives. N₂ reduction reaction (NRR) and nitrate reduction reaction (NO₃⁻RR) are two potential approaches for electrochemical NH₃ synthesis. However, the existing research foundation still faces challenges in achieving high selectivity and efficiency. Direct NH₃ FC are easy to transport and are expected to be widely used in mobile energy consuming equipment, but also limited by the lack of highly active and stable NH₃ oxidation electrocatalysts. The perspectives of ammonia fuel cells as an alternative green energy are discussed.