A just energy transition (JET) to low-carbon fuels, such as green hydrogen, is critical for mitigating climate change. Countries with abundant renewable energy resources are well-positioned to meet the growing global demand for green hydrogen. However, to improve the volumetric energy density and facilitate transport and distribution over long distances, green hydrogen needs to be converted into an energy carrier such as green ammonia. This study conducted a comparative life cycle assessment (LCA) to evaluate the environmental impacts of green ammonia production, with a particular focus on greenhouse gas (GHG) emissions. The boundary of the study was from cradle-to-production gate, and the design was based on a coastal production facility in South Africa, which uses renewable energy to desalinate seawater, produce hydrogen, and synthesise ammonia. The carbon intensity of production was 0.79 kg CO₂-eq per kg of ammonia. However, if co-products of oxygen, argon and excess electricity are sold to market and allocated a portion of GHG emissions, the carbon intensity was 0.28 kg CO₂-eq per kg of ammonia. Further, without the sale of co-products but excluding the embodied emissions of the energy supply system, as defined in the recent international standard (ISO/TS 19870), the carbon intensity was 0.11 kg CO₂-eq per kg of ammonia. Based on the hydrogen content of ammonia, this is equivalent to 0.60 kg CO₂-eq per kg of hydrogen, which is well below the current threshold for certification as a low-carbon fuel. The process contributing most to the overall environmental impacts was electrolysis (68%), with particulate matter (55%) and global warming potential (33%) as the dominant impact categories. This reflects the energy intensity of electrolysis and the carbon intensity of the energy used to manufacture the infrastructure and capital goods required for green ammonia production. These findings support the adoption of green ammonia as a low-carbon fuel to mitigate climate change and help achieve net-zero carbon emissions by 2050. However, achieving this goal requires the rapid decarbonisation of energy supply systems to reduce embodied emissions from manufacturing infrastructure.

Hydrogen is a promising energy carrier that is expected to play a crucial role in helping Canada achieve its net-zero target by 2050. However, reducing the ambiguity in regulatory frameworks is essential to incentivize and facilitate international trade in hydrogen. To this end, regulators must agree on quantification methodologies that consider life cycle boundaries, process descriptions, co-product allocation, conversion constants, and certification units. Several studies have highlighted the importance of life cycle assessment (LCA) as a standardized, relevant method for estimating the carbon footprint associated with hydrogen production and evaluating its environmental sustainability. As such, LCA-based certification schemes could help create a transparent hydrogen market. The aim of this study is to validate the proposed harmonized LCA-based methodology for quantifying hydrogen production’s carbon intensity. This methodology follows a consistent scope and life cycle inventory (LCI) development criteria, alongside a rigorous data quality assessment. The well-to-gate carbon intensities of six hydrogen production pathways are compared, which range from 0.26 to 10.07 kg CO_2e per kg of hydrogen (kg CO_2e/kg H₂), against the hydrogen carbon intensity thresholds established by the Canadian Clean Hydrogen Investment Tax Credit (CHITC). For example, the biomass gasification with carbon capture (CC) pathway demonstrates the lowest carbon intensity, while thermochemical pathways, such as steam methane reforming of natural gas without CC, poses challenges to meeting the maximum CHTIC threshold of 4 kg CO_2e/kg H₂.

Silicon nitride (Si₃N₄) is an excellent candidate for engineering ceramics; however, its toughness and hardness are fundamentally limited by the inherent incompatibility between the hard α-phase and the tough β-phase. Si₃N₄ ceramics with a columnar-cluster microstructure are reported, achieving combination of toughness of 10.2 ± 0.3 MPa·m^1/2and 20.1 ± 0.3 GPa hardness. Those values represent the state-of-the-art among Si₃N₄ ceramics fabricated via liquid-phase sintering reported to date. The formation of the columnar clusters is driven by a high-pressure-induced coarsening process. The metastable growth mechanism may open a new pathway for preparing a new generation of Si₃N₄ ceramics with superior performance.