Abstract:

Green Hydrogen-Ammonia cycle refers to a promising chain for energy storage and transportation through the mutual conversion of hydrogen-ammonia. This cycle primarily includes Green Hydrogen to Ammonia (H2A) and Green Ammonia to Hydrogen (A2H). It aims to address the high energy consumption and excessive carbon dioxide emissions associated with the Haber-Bosch process for ammonia synthesis, while also tackling the challenges of hydrogen storage and transportation at high pressure within the hydrogen supply chain. Moreover, this cycle plays a vital role in connecting renewables, hydrogen, ammonia, and traditional industries such as iron and steel industry, promoting the efficient use of renewable resources. In the H2A phase, current research focuses on exploring new technologies, including catalysts, to synthesize ammonia under ambient conditions towards achieving industrial-scale production as an alternative to the Haber-Bosch method. However, challenges such as long-term stability still need to be addressed. To ensure the effective operation of the green cycle, the A2H must be efficient to split ammonia back into hydrogen for both direct and indirect uses, such as generating renewable electricity. A comprehensive understanding of ammonia synthesis and decomposition reactions is essential for a deeper insight into the Hydrogen-Ammonia cycle, as the H2A and A2H processes are reversible. In this review, we first explain the Hydrogen-Ammonia green cycle and then highlight the latest advancements in research on H2A and A2H driven by renewable energy under ambient conditions. Additionally, we endeavor to provide forward-looking insights into the future of the green Hydrogen-Ammonia cycle.

Key words: hydrogen production, ammonia synthesis, ammonia decomposition, renewable energy, catalysis

摘要：

氢-氨绿色循环是指利用氢和氨的相互转换来实现能源的存储和运输，这个过程主要包括绿氢制氨（hydrogen to ammonia，H2A）与绿氨制氢（ammonia to hydrogen，A2H）。该循环不仅有望解决传统Haber-Bosch工艺合成氨的高能耗与过量CO₂排放问题，还可能为氢能产业链中高压氢气储存与运输的挑战提供可行性方案，成为贯通可再生能源、氢能、氨能和传统产业如钢铁行业的重要环节，促进资源的高效利用。在H2A过程中，当前的研究主要集中在中低温、室温条件下的合成氨工艺以期取代Haber-Bosch法，但这些工艺面临诸多尚待解决的科学挑战。此外，氢-氨绿色循环的顺利运行依赖于氨的有效能量释放，即A2H过程的有效进行，以确保氨分解为氢气和/或直接将氨转化为电力或能量。H2A与A2H互为可逆过程，全面理解氨合成与氨分解反应对于更深入与全面理解氢-氨循环十分重要。因此，本文将立足氢-氨循环，首先简要介绍氢与氨之间的关系，随后着重总结当前利用可再生能源驱动的中低温、室温条件下的H2A和A2H研究的最新进展。最后，总结了目前氢-氨绿色循环的进程及面临的挑战，并对该领域未来的发展方向进行展望。

关键词: 制氢, 氨合成, 氨分解, 再生能源, 催化