Global warming and its cause and effects have necessitated the researchers to look beyond fossil and its derivatives. The scalability of CO2 reduction and H2 energy is one of the most enigmatic questions asked by the calamitous environmental changes happening across the world such as bushfires in Australia, Amazon and California or the melting of Arctic and Antarctic ice scalps. Thus, the research fraternity is keen to elevate the efficiency of CO2 reduction and H2 energy to the extent that the good chemical livestock produced by CO2 conversion and H2 fuel would become principal energy resources. In this quest, photocatalytic pathway envisions the environmentally benign protocol to bring about CO2 reduction and H2 production. Photo‐reduction of CO2 and H2 generation via photocatalytic water splitting by utilizing oxide based heterostructured photocatalysts are the promising approaches to carry out CO2 mitigation and H2 production efficiently ascribed to the advanced optoelectronic and structural superiority of oxides photocatalysts as discussed in this review.

Developing a unique catalytic system with enhanced activity is the topmost priority in the science of H2 energy to reduce costs in large-scale applications, such as automobiles and domestic sectors. Researchers are striving to design an effective catalytic system capable of significantly accelerating H2 production efficiency through green pathways, such as photochemical, electrochemical, and photoelectrochemical routes. Bi-based nanocatalysts are relatively cost-effective and environmentally benign materials which possess advanced optoelectronic properties. However, these nanocatalysts suffer back recombination reactions during photochemical and photoelectrochemical operations which impede their catalytic efficiency. However, heterojunction formation allows the separation of electron–hole pairs to avoid recombination via interfacial charge transfer. Thus, synergetic effects between the Bi-based heterostructured nanocatalysts largely improves the course of H2 generation. Here, we propose the systematic review of Bi-based heterostructured nanocatalysts, highlighting an in-depth discussion of various exceptional heterostructures, such as TiO2/BiWO6, BiWO6/Bi2S3, Bi2WO6/BiVO4, Bi2O3/Bi2WO6, ZnIn2S4/BiVO4, Bi2O3/Bi2MoO6, etc. The reviewed heterostructures exhibit excellent H2 evolution efficiency, ascribed to their higher stability, more exposed active sites, controlled morphology, and remarkable band-gap tunability. We adopted a slightly different approach for reviewing Bi-based heterostructures, compiling them according to their applicability in H2 energy and discussing challenges, prospects, and guidance to develop better and more efficient nanocatalytic systems.

The global climate crisis has cultivated the demand for sustainable energy resources as fossil derivative fuels are functional in catalyzing the rate of environmental breakdown. Sustainable energy solutions generate various renewable energy prospects capable of delivering efficient energy operations. Among these prospects, green H2 energy generated via overall water splitting is an effective approach towards sustainability ascribed to the higher gravimetric density and efficiency of H2 fuel. In this review, we sought to discuss the applicability and challenges of graphene-based derivatives in H2 evolution operations through photochemical, electrochemical and photoelectrochemical water-splitting pathways. The unique layered structure of graphene-based derivatives alongside marvelous optoelectronic and physicochemical properties ease out the thermodynamic uphill of water splitting better than their non-layered counterparts. In addition, the heterojunction formation in the graphene derivatives with visible light catalysts propels the kinetics of HER. Functionalized GO and rGO derivatives of graphene are riveting catalysts that have received extensive interest from researchers attributed to their accelerated chemical and mechanical stability, tunable band structure and larger surface area, providing more exposed active sites for HER. The surface organic functional groups of GO/rGO assist in establishing synergetic interfacial contact with other catalysts. Thus, these groups provide structural and chemical versatility to GO/rGO-based heterostructured catalysts, which effectively improve their physicochemical parameters that drive their catalytic performance towards HER. In order to develop a cost-effective and highly efficient catalytic system, graphene-based derivatives are promising heterostructured catalysts that exhibit a good relationship between catalytic efficiency and robustness.

Global energy crisis has encouraged the need for sustainable energy resources, which is the viable alternate of providing effective energy operations and considered as remedy for the ongoing energy crisis. Development in the science and technology eases out plenty of issues that were once thought to be uphill. Presently, earth is being subjected to several grave issues which need to be addressed as soon as possible. Nuclear and hydrogen energy are the important areas which promise the optimistic way of handling the existential energy crisis due to cost, scarcity of resources and unavailability of considerable feedstock. Ceramics are the diverse inorganic materials which offer tremendous chemical and physical characteristics. Due to their structural, compositional and morphological versatility, advanced ceramics based hybrid materials can be exploited in nuclear and hydrogen energy applications as discussed in this review. Extensive survey outlined the applicability of ceramics in various nuclear science based applications as they include fissionable species and possess higher thermal conductivity, their enormous resistance towards radiation and refractoriness in fuels and in waste residuals due to their potential to hold radio nuclides and surveyed the scope of several metal oxides ceramics in carrying out hydrogen energy operations via overall water splitting.