Scaling up photocatalytic systems for large-scale hydrogen generation holds transformative potential for sustainable energy but faces significant technical and economic challenges in transitioning from lab-scale experiments to industrial applications. This review delves into recent innovations that drive progress in this field, including advanced materials developed for improved efficiency and stability, as well as innovative reactor designs that optimize light capture and reactant flow. It also examines practical strategies for the integration of these systems with renewable energy sources, focusing on their scalability and cost-effectiveness. Key challenges addressed include mass transport limitations, reactant utilization, and catalyst longevity, accompanied by emerging solutions that aim to overcome these hurdles. The review comprehensively explores the intersection of technological advancements and economic feasibility, emphasizing environmental and economic considerations necessary for the practical implementation of photocatalytic hydrogen production. Emphasizing the most recent developments and strategic approaches, this review outlines a pathway for advancing large-scale sustainable hydrogen generation technologies.

Electro-oxidation of urea (UOR) in alkaline medium is one of the most effective alternative ways of producing green hydrogen, as the oxidation potential in UOR is less and thermodynamically more favorable than conventional water oxidation. The development of cost-effective materials in catalyzing UOR is recently seeking more attention in the research hotspot. Suitably modifying the Ni-based catalysts towards active site creation and preventing surface passivation is much important in this context, following which we reported the synthesis of Ni₃S₂ (NS) supported with CuCo (CC) bimetallic (NSCC). A simple hydrothermal route for NS synthesis and the electrodeposition method for CuCo (CC) deposition is adapted in a self-supported manner. The NS and CC catalysts exhibited sheet-like morphology, as confirmed by SEM and TEM analysis. The bimetallic CC deposition prevented the surface passivation of nickel sulfide (NS) over oxygen evolution reaction (OER) and improved the charge-transfer kinetics. The NSCC catalyst catalyzed UOR in an alkaline medium, which required a lower potential of 1.335 V vs. RHE to attain the current density of 10 mAcm⁻², with a lower Tafel slope value of 131 mVdec⁻¹. In addition, a two-electrode cell setup is constructed with an operating cell voltage of 1.512 V for delivering 10 mAcm⁻² current density. This study illustrates the new strategy of designing heterostructure catalysts for electrocatalytic UOR.

Transition metal-based layered double hydroxides (LDHs) have gained an attractive interest among two-dimensional (2D) materials because they offer tunable structure, abundant active sites, and superior stability for carbon-dioxide (CO2) reduction. Recently, defect engineering, particularly transition metal vacancies, acted as the most important defects in enhancing the bifunctional catalytic activity of LDHs both in photocatalysis and electrocatalysis. This review explores the critical role that transition metal vacancies and defects play in improving CO2 adsorption, activation, and charge transfer processes, which in turn enhance catalytic performance. The interaction between defect engineering and LDHs electronic structure is examined, providing insight into the processes that support multi-electron transfer pathways and stabilize reaction intermediates. Furthermore, generating defects in layered double hydroxides and advanced spectroscopic techniques such as XAS, ESR, and PAS for defect-driven catalytic behavior are discussed. This review demonstrates the ground-breaking potential of defect-engineered LDHs in creating sustainable, dual-functional catalytic systems for CO2 reduction by tackling the problems of stability, scalability, and defect control. The insights provided in this review aim to inspire innovative approaches for the design of next-generation catalysts, paving the way for effective carbon capture and conversion technologies.