The conventional Haber-Bosch process, which supplies nearly all of the world’s ammonia, operates under extreme heat and pressure, consuming about 1–2% of global energy and releasing roughly 1.6 tons of CO2 per ton of ammonia produced.
Schematic of the HAHS-mediated nitrogen reduction pathway on Co(OH)2. Image Credit: Chinese Academy of Sciences
Electrocatalytic nitrogen reduction, driven by renewable electricity, promises a sustainable alternative – but the strong N≡N bond (bond dissociation energy of 941 kJ/mol) makes N2 activation exceptionally difficult. Existing associative pathways suffer from either premature hydrazine release or high activation barriers, leading to poor selectivity and sluggish kinetics. Based on these challenges, there is an urgent need for in-depth research into novel reaction mechanisms that can lower energy barriers, suppress the competing hydrogen evolution reaction, and unlock practical ambient-condition ammonia synthesis.
A team from Qingdao Agricultural University (China), Politecnico di Milano (Italy), and Trinity College Dublin (Ireland) has developed a cobalt hydroxide catalyst that enables a new reaction pathway for nitrogen reduction. Their findings, published (DOI: 10.1016/j.esci.2025.100513) on September, 2026, in eScience, demonstrate a record-high ammonia yield rate of 40.67 μg h-1 cm-2 with a Faradaic efficiency of 24.9% – marking a significant step toward sustainable, decarbonized fertilizer production.
The key innovation lies in a mechanism the team calls “hydroxide-activated hydrogen spillover” (HAHS). By precisely controlling synthesis temperature, the researchers introduced targeted lattice distortion into the Co(OH)2 catalyst, elongating Co–O bonds and weakening adjacent O–H bonds. This structural tuning allows hydrogen atoms from the surface hydroxyl groups to detach and participate directly in the nitrogen reduction reaction, dynamically generating surface hydrogen vacancies. These vacancies are continuously replenished by hydrogen species from the electrolyte, creating a self-sustaining catalytic cycle. Unlike conventional associative pathways that require multiple proton-coupled electron transfer steps, the HAHS mechanism bypasses one elementary step entirely, accelerating intermediate turnover and suppressing the competing hydrogen evolution reaction. Density functional theory calculations confirmed that the initial N2 activation on Co(OH)2 is nearly barrierless (ΔG = 0.01 eV), while the catalyst maintained exceptional structural integrity over 180 hours of continuous operation. In situ electron spin resonance and isotope-labeled differential electrochemical mass spectrometry provided direct experimental evidence for hydrogen spillover and vacancy formation, validating the proposed mechanism.
The authors said the HAHS mechanism fundamentally changes how we think about nitrogen reduction. They explained that instead of fighting against the competing hydrogen evolution reaction, their approach actually harnesses hydrogen from the catalyst itself to drive the reaction forward. They added that the lattice distortion engineering gives them precise control over bond strengths, allowing them to tune the catalyst’s behavior at the atomic level. They described this as a new paradigm for designing electrocatalysts – one that could be applied beyond ammonia synthesis to other complex multi-step reactions.
This approach could accelerate the transition to distributed, on-site ammonia production for fertilizer, reducing reliance on centralized Haber-Bosch plants and their associated CO2 emissions. The ambient-condition operation aligns perfectly with renewable energy sources, enabling green ammonia synthesis directly from air, water, and electricity. Beyond agriculture, ammonia is also gaining traction as a carbon-free hydrogen carrier for energy storage and transportation. The HAHS mechanism, enabled by simple lattice engineering, offers a scalable and cost-effective strategy that could bring electrochemical ammonia synthesis closer to industrial reality – supporting both food security and global decarbonization goals.