This work presents a comprehensive computational investigation of a novel two‐dimensional (2D) organic carbon nitride (C 5 N) monolayer for hydrogen (H 2 ) storage applications. Van der Waals‐corrected density functional theory calculations reveal that pristine C 5 N interacts weakly with H 2 molecules, thereby limiting its storage capability. To address this limitation, the C 5 N monolayer is functionalized with light alkali metals M (M = Li, Na, and K) to enhance its adsorption performance. Energetic analysis demonstrates that C 5 N can stably accommodate up to six metal dopants, with average binding energies of −2.88, −1.84, and −1.80 eV per dopant for Li, Na, and K, respectively. These values are significantly stronger than the corresponding cohesive energies of the dopants, thus preventing metal aggregation. The thermal stability of the functionalized systems is confirmed through ab initio molecular dynamics simulations at 300 K. Electronic structure and charge analysis, based on projected density of states and Bader charge calculations, indicate charge transfer values of 0.99, 0.99, and 0.85 electrons per dopant from Li, Na, and K to the C 5 N monolayer, respectively. This charge transfer leads to enhanced polarization, reduced bandgap, and improved H 2 adsorption performance. Each metal dopant can adsorb up to eight H 2 molecules, leading to a maximum storage capacity of 48 H 2 molecules per unit cell. The corresponding gravimetric densities are 9.42, 8.61, and 7.93 wt% for the Li‐, Na‐, and K‐functionalized C 5 N systems, respectively, with moderate average adsorption energies (−0.16 to −0.17 eV/H 2 ) that are suitable for reversible H 2 storage. Thermodynamic analysis under practical fuel‐cell operating temperature and pressure conditions further confirms the favorable H 2 adsorption/desorption behavior of the functionalized C 5 N systems. The reversibility of the designed materials is evaluated through desorption temperature and recovery time calculations, indicating efficient H 2 release kinetics. In addition, volumetric storage performance is assessed through density‐to‐volume ratio analysis. Overall, these results highlight alkali metal‐functionalized C 5 N monolayers as promising candidates for efficient and reversible H 2 storage applications.
The development of sustainable and high‐performance electrochemical energy‐storage systems requires electrode materials capable of combining fast charge transfer, high power capability and long‐term stability. In this context, pseudocapacitive transition metal oxides have attracted increasing attention due to their ability to bridge the gap between conventional capacitors and batteries. Herein, a sustainable surface‐engineering strategy is proposed to enhance the pseudocapacitive response of hexagonal WO 3 nanoparticles through in situ functionalization with N‐ and S‐containing species during a simple aqueous hydrothermal synthesis. The introduced surface functionalities improve the electrochemical performance without altering the bulk crystal structure or morphology of WO 3 . In particular, the functionalized materials exhibit enhanced specific capacitance, improved coulombic efficiency, and remarkable cycling stability over 10,000 cycles, with S‐functionalized WO 3 showing the best overall response. Spectroscopic analyses suggest that surface electronic modulation and more favorable interfacial charge–transfer processes contribute to the improved pseudocapacitive behavior. Moreover, the exclusive use of aqueous synthesis, water‐based electrode processing, and aqueous electrolytes provides a greener route toward electrode fabrication. These findings highlight surface functionalization as a promising and sustainable strategy for tuning the interfacial properties of WO 3 ‐based electrodes for next‐generation energy‐storage technologies.
The development of sustainable and high‐performance electrochemical energy‐storage systems requires electrode materials capable of combining fast charge transfer, high power capability and long‐term stability. In this context, pseudocapacitive transition metal oxides have attracted increasing attention due to their ability to bridge the gap between conventional capacitors and batteries. Herein, a sustainable surface‐engineering strategy is proposed to enhance the pseudocapacitive response of hexagonal WO3 nanoparticles through in situ functionalization with N‐ and S‐containing species during a simple aqueous hydrothermal synthesis. The introduced surface functionalities improve the electrochemical performance without altering the bulk crystal structure or morphology of WO3. In particular, the functionalized materials exhibit enhanced specific capacitance, improved coulombic efficiency, and remarkable cycling stability over 10,000 cycles, with S‐functionalized WO3 showing the best overall response. Spectroscopic analyses suggest that surface electronic modulation and more favorable interfacial charge–transfer processes contribute to the improved pseudocapacitive behavior. Moreover, the exclusive use of aqueous synthesis, water‐based electrode processing, and aqueous electrolytes provides a greener route toward electrode fabrication. These findings highlight surface functionalization as a promising and sustainable strategy for tuning the interfacial properties of WO3‐based electrodes for next‐generation energy‐storage technologies.
Solar energy is inherently intermittent, and as demand grows for dependable low‐carbon power, efficient storage is essential to the sustainable energy transition and long‐term energy security. Yet most reviews examine these technologies in isolation rather than comparing them directly. This study compares six leading routes for storing solar energy: sensible heat, latent heat, thermochemical, electrochemical, supercapacitor, and large‐scale mechanical systems. Each is assessed within a single framework spanning thermodynamic performance, storage density, operating temperature, efficiency, commercial readiness, and application suitability. The thermal technologies differ markedly. Sensible heat storage reaches efficiencies of 50%–90% but has low storage density (~0.18 GJ m−3), latent heat storage holds nearly 2.5 times more energy than a conventional water tank (150–200 kJ kg−1), and thermochemical storage achieves the highest density (~1.8 GJ m−3) with very low standby losses, making it suitable for seasonal use. Among nonthermal options, lithium‐ion batteries deliver 85%–95% round‐trip efficiency, supercapacitors exceed 90% over 30,000 cycles, and pumped hydro sustains 70%–85% at grid scale. Overall, hybrid systems integrating thermal, electrochemical, hydrogen, and mechanical pathways offer the most promising route to dispatchable renewable power.
Spent transformer oil (STO) represents a complex industrial liquid waste that poses significant environmental challenges. In this work, STO was converted into hydrogen‐rich synthesis gas via catalytic microwave‐induced steam reforming over monometallic (10%Ni/diatomite, 10%Co/diatomite) and bimetallic (5%Ni5%Co/diatomite) catalysts. The diatomite contained an inherent Fe2O3 content of about 9.25 wt.%, which likely contributed to the catalytic activity in addition to its role as a thermally stable and porous support. The operating conditions were optimized without catalyst, and increasing the microwave power from 600 to 840 W and the steam‐to‐carbon ratio up to 3.6 enhanced both the H2 yield and carbon conversion through the promotion of endothermic reforming reactions. Among the catalysts tested, the bimetallic 5%Ni5%Co/diatomite achieved the highest H2 yield of 98.80 mmol g−1STO and carbon conversion of 70.58%, with a H2/CO ratio of 2.83. The initially oxidized metals were reduced in situ to a metallic Ni─Co alloy during the reaction. Collectively, these findings highlight the potential of Fe‐rich diatomite as a low‐cost, naturally abundant support for converting hazardous waste oil into hydrogen‐rich syngas via microwave‐induced steam reforming.
