Gas bubbles generated at electrode surfaces influence water-splitting efficiency by modifying the electrochemically active area, ionic transport pathways, local mass transfer, and interfacial resistance. Among the coupled stages of bubble nucleation, growth, coalescence, and departure, bubble coalescence is particularly important because it can redirect post-coalescence bubble responses, including pinned retention, attached lateral relocation, transient lift-off and return, complete departure, and collective oscillatory growth mediated by mother-bubble/bubble-carpet interactions. These responses occur across multiple length scales, from pressure-energy-dominated nanobubble coalescence to surface-energy-mediated microbubble interactions and collective mother-bubble/bubble-carpet dynamics. In this review, bubble coalescence in electrochemical and photoelectrochemical water splitting is examined from the perspectives of interfacial mechanism, transport coupling, and performance implications, drawing selectively on studies of other multiphase systems for fundamental mechanistic insights. Recent theoretical models, high-resolution experimental observations, and mechanistic interpretations are compared, with particular attention paid to the conditions under which coalescence promotes complete bubble departure, induces interfacial renewal, enhances local convection, or instead causes persistent surface blockage. Strategies for regulating coalescence behavior are further discussed, including electrolyte engineering based on ion-specific effects, bubble–bubble interaction design, multiscale electrode architectures, and ultrasound-assisted bubble control. Bubble coalescence is therefore presented not as an intrinsically beneficial or detrimental event, but as a controllable interfacial process whose electrochemical effect depends on the resulting post-coalescence pathway. Finally, design criteria for gas-evolving electrodes and operating conditions are discussed in relation to departure-favorable coalescence and high-current-density water splitting.
Global warming represents a significant environmental challenge, prompting extensive research into Carbon Capture, Utilization, and Storage (CCUS) technologies. Calcium oxide (CaO)-based sorbents, particularly within the Calcium Looping (CaL) process, have emerged as a primary focus for high-temperature post-combustion CO2 capture and thermochemical energy storage (TCES). To address sintering and sustain sorbent performance over multiple CaL cycles, various enhancement strategies for nanostructured and granule-shaped CaO have been developed. Nevertheless, comprehensive reviews of recent advancements remain limited, underscoring the necessity to critically assess these developments for practical implementation. To this end, a timely review is required to identify the more sophisticated and efficient method for developing the best structurally operational CaO sorbents, considering all effective operational and structural conditions. This study, motivated by the significant impact of CaO texture on its CO2 capture activity and TCES performance, first examines conventional CaO-based preparation methodologies, followed by a systematic analysis of contemporary advancements in the development of modified sorbents. Particular emphasis is placed on comprehensively evaluating optimized modification strategies for enhanced CO2 capture capacity. This review thoroughly examines the CO2 capture capacity and TCES potential of modified CaO powders and granules to assess the effectiveness of different textural and functional improvements. It systematically compares the performance of various enhancement methods for nanostructured and granule-shaped CaO sorbents under laboratory and semi-practical conditions. The paper also discusses latest advances in improving the fluidity of CaO-based sorbents in fluidized-bed systems are also discussed, along with recent developments in using CaL for TCES. Persistent issues like sorbent sintering are addressed through strategies such as doping, particle design, and advanced synthesis, offering a comprehensive outlook on the progress and future prospects of CaL technology.
Achieving Net-Zero emissions by 2050 and mitigating climate change demand efficient catalytic conversion of CO2 into valuable chemicals and fuels, a cornerstone for a sustainable circular carbon economy. This review comprehensively summarizes recent progress and critical catalyst properties in key thermal heterogeneous CO2 conversion processes, specifically dry reforming of methane, reverse water-gas shift, CO2-to-methanol synthesis, and the Sabatier reaction. For dry reforming of methane, overcoming coke deposition and metal sintering through optimized oxygen storage capacity, metal dispersion, and catalyst morphology is essential. In the reverse water-gas shift reaction, noble metal catalysts supported on reducible oxides exhibit superior intrinsic activity, but developing stable, cost-effective alternatives such as Mo-based transition metal carbides and dual-functional single-atom catalysts is imperative. CO2-to-methanol synthesis critically relies on precise engineering of metal–oxide interfaces and oxygen vacancies, with In2O3-based catalysts and strategic vacancy engineering demonstrating high potential. The Sabatier reaction, predominantly using Ni-based catalysts, requires improved catalytic stability and activity through advanced morphology control, incorporation of secondary metals, and alternative energy-assisted methods (e.g., plasma, mechanochemical).Overall, continued emphasis on catalyst–physicochemical property relationships, scalable synthesis, alternative energy integration, and techno-economic analyses will drive advances towards practical and efficient catalytic CO2 conversion within a circular carbon economy framework.
The substantial increase in CO2 emissions from various point sources has become a major contributor to the greenhouse effect, intensifying global warming and exacerbating climate instability. Addressing the rising levels of atmospheric CO2 requires innovative and sustainable mitigation strategies. Integrated carbon capture and conversion (ICCC) is an emerging approach that enables the simultaneous capture and conversion of CO2 into intermediates, such as methane (CH4), carbon monoxide (CO), and syngas, via methanation, reverse water-gas shift (RWGS), and dry reforming of methane (DRM). These intermediates can be further upgraded into value-added liquid fuels via methanol synthesis or the Fischer-Tropsch route, directly supporting the production of renewable methanol and SAF. ICCC could potentially reduce the need for CO2 compression and transport, may lower the energy-intensive requirements for sorbent regeneration, and reduce the reactor systems typically associated with conventional processes. This review critically examines advancements in ICCC technologies, focusing on the design and optimization of dual-function materials (DFMs) and the synergistic interactions between adsorbents and catalysts. It explores optimized reaction pathways, material stability, and the techno-economic feasibility of ICCC systems, while addressing the effects of key operational parameters. Challenges such as thermal sintering, catalyst deactivation, and impurities (e.g., O2, H2O, sulfur species) are addressed. Practical implementation issues, including gas switching between oxidising and reducing atmospheres, purge losses, H2 utilization, product dilution and cyclic reactor heat management, are also discussed as critical determinants of scale-up feasibility. By integrating insights from materials science, process engineering, and economic analysis, this study identifies the material and process conditions under which ICCC may offer advantages over separated capture and conversion routes. The review also highlights that practical deployment remains conditional on long-term DFM stability, realistic gas switching, impurity tolerance, low-carbon H2 availability, heat integration, and reactor-scale validation.
Over the past decade, the pursuit of rapid, scalable, and cost-effective graphene synthesis strategies has intensified, driven primarily by graphene's exceptional structural, electrical, and thermal properties, which underpin its transformative potential in energy storage, electronics, and sensing. However, conventional synthesis methods (e.g., chemical vapor deposition [CVD] and exfoliation) suffer from inherent bottlenecks, including high mass-production costs and limited scalability, making rapid, energy-efficient, and scalable graphene manufacturing an increasingly critical priority to meet the accelerating demand for high-performance carbon materials. This review systematically examines three emerging non-conventional synthesis platforms, direct laser writing (DLW), Joule heating (JH), and atmospheric-pressure plasma (APP) and highlights their distinctive advantages (e.g., rapid processing, feedstock versatility, intrinsic process intensification) and inherent limitations relative to conventional CVD and exfoliation routes. A unified mechanistic analysis is presented, focusing on localized thermofluidic behavior, ultrafast nonequilibrium carbon transformations, defect evolution pathways, and graphitic domain formation across these techniques. Structure–property correlations relevant to energy storage devices, including supercapacitors and various battery systems, are systematically discussed. The review further highlights key challenges in achieving process uniformity, mechanistic predictability, and industrial scalability, while outlining timely opportunities for advancing these methods through integration with emerging reactor concepts, sustainable carbon feedstocks, and hybrid manufacturing strategies. Collectively, these insights position DLW, JH, and APP as promising cornerstones for next-generation rapid graphene synthesis, and this work aims to provide a comprehensive perspective to inspire innovations in process design and mechanistic understanding.
