Next generation materials for sustainable energy and environmental solutions.

The oxygen evolution reaction (OER), a key half-reaction in electrochemical water splitting, is limited by sluggish multi-electron transfer kinetics, starting extensive research into efficient, low-cost nanoscale electrocatalysts, particularly those based on nickel, cobalt, and iron, as well as mixed-metal, hybrid, and heteroatom-doped carbon-based metal-free systems, as presented here. Ni- and Co-based electrocatalysts show high efficiency for alkaline OER due to optimized nanostructures, surface modifications, heterostructure design, and multi-metal doping, which enhance activity, stability, and electronic properties. Their performance relies on precise atomic-level control of structure and synergistic interactions, enabling them to approach or rival noble-metal catalysts. Iron-based electrocatalysts are also promising due to their abundance, low cost, and flexible redox chemistry, forming active iron oxyhydroxide species during operation; however, their low conductivity requires structural and electronic optimization. Beyond Fe, Ni, and Co, copper-based compounds, zeolitic imidazolate framework-derived structures, and manganese phosphide–cerium oxide composites offer enhanced oxygen vacancies, tunable structures, and strong interfacial synergy. Furthermore, heteroatom-doped carbon materials incorporating nitrogen, phosphorus, or sulfur improve catalytic activity by modifying electronic structure, creating active sites, and enhancing charge transfer. Overall, careful control of composition, structure, and electronic properties enables the development of efficient, durable, and scalable noble-metal-free catalysts for OER.

The oxygen reduction reaction (ORR) is a key process in electrochemical energy conversion technologies such as fuel cells and metal–air batteries; however, its sluggish kinetics and reliance on precious metal catalysts limit large-scale application. This review provides a comprehensive overview of recent advances in non-precious nanoscale electrocatalysts for ORR in alkaline media. Particular emphasis is placed on reaction mechanisms, including dominant pathways, kinetics, and key intermediates, as well as the advantages of alkaline electrolytes over acidic systems. The performance of various catalyst classes is systematically discussed, including transition metal-based materials (Fe, Co, Zn, Cu, and bimetallic systems) and metal-free carbon-based electrocatalysts. Special attention is given to heteroatom-doped carbon materials, carbon nanostructures, and emerging hybrid systems such as MXene-based composites. Comparative analysis highlights the relationship between catalyst composition, structure, and electrochemical performance metrics, including half-wave potential, onset potential, Tafel slope, number of electron transfer, and operational stability. Overall, non-precious catalysts demonstrate promising activity and durability, approaching that of noble metals under alkaline conditions. The insights summarized in this review guide the rational design of efficient, cost-effective ORR electrocatalysts and support the development of sustainable energy technologies.

The global transition to low-carbon energy systems has intensified interest in hydrogen as a clean energy carrier. Still, the environmental benefits of using hydrogen as a fuel depend greatly on its production process, as conventional fossil-fuel-based methods are associated with significant greenhouse gas emissions. In this regard, hydrogen production from renewable energy (so-called green hydrogen) has emerged as a promising solution for sustainable energy systems. This study evaluates water electrolysis powered by renewable electricity from solar, wind, hydroelectric, and geothermal sources alongside thermochemical and biological hydrogen production from biomass. Solar- and wind-based electrolysis currently offers the most favorable balance between technological maturity, scalability, and cost, with levelized costs ranging from about 3.8 to 11.9 USD/kg H₂ depending on resource quality and electricity price. Conversely, biomass-based processes operate more efficiently but face material and sustainability limitations. Emerging technologies (e.g., offshore wind-energy-powered water electrolysis) show significant long-term potential but remain constrained by low maturity. This paper highlights key challenges and future research directions needed to accelerate the transition to a sustainable hydrogen economy.

Hydrogen, with its high gravimetric energy density (≈120 MJ kg-1) and no carbon dioxide emissions from combustion or electrochemical oxidation, is a key element for decarbonization and the integration of renewable energy sources. However, its low volumetric density at ambient conditions (0.0899 kg m-3) requires efficient, safe, and economically acceptable storage solutions. This review paper synthesizes the latest methods for physical, solid-state, and geological hydrogen storage, drawing on advances in materials science and techno-economic assessment. Special emphasis is placed on the trade-offs among gravimetric/volumetric densities, efficiency, technology maturity, and scalability to guide technology selection for applications in transport, industry, and grid systems.