Review of Recent Progress in Green Ammonia Synthesis : Decarbonisation of fertiliser and fuels via green synthesis

Most of the global production of ammonia requires fossil fuels and is associated with considerable greenhouse gas emissions. Replacing fossil fuel ammonia with green or zero-carbon ammonia is a major focus for academia, industry and governments. Ammonia is a key component in fertiliser but is also attracting increasing interest as a carbon-free fuel for the maritime sector and as a hydrogen vector. This review describes the use of green (electrolysed) hydrogen in conventional Haber-Bosch plants and predicts adoption of the technology by 2030. Further into the future, direct green ammonia synthesis by electrocatalytic and photocatalytic means may present a cost-effective alternative to the Haber-Bosch process. Electrocatalytic and photocatalytic routes to ammonia are reviewed, the catalytic systems are compared and their potential for meeting the likely demand and cost for ammonia considered.