Qian Xu

Large-scale alkaline water electrolysis (AWE) is essential for green hydrogen production, yet coupled multiphysics transport in industrial-scale cells remains insufficiently understood. A multiphysics model is developed for zero-gap AWE cells with different diameters. The anisotropic permeabilities of support meshes are determined via pore-scale simulations and incorporated into a REV-scale model coupling two-phase flow, species transport, electrochemistry, and heat transfer. The model is validated against a 5 MW commercial system with a mean relative error below 3%. The anode support mesh exhibits non-negligible permeability anisotropy. Under identical current density and flow coefficient, larger-diameter cells show higher electrochemical efficiency due to enhanced bubble removal. Increasing flow rate reduces gas blockage and improves two-phase uniformity, but with diminishing returns for large cells. For single-inlet/single-outlet configurations, varying flow rate alone cannot improve concentration and temperature uniformity. The multi-inlet design reduces top gas accumulation when the primary-to-secondary flow ratio is controlled; excessive secondary flow deteriorates uniformity. The multi-outlet design moderately improves gas removal but significantly enhances concentration and temperature uniformity, reducing dissolved hydrogen accumulation and improving safety. These flow-field optimizations are expected to help mitigate bubble-induced active-site loss and reduce local overpotential, thereby benefiting HER/OER catalyst performance. These findings support scale-up design and flow-field optimization of industrial AWE cells.

Neutral iron-sulfur flow batteries feature low cost, high safety and environmental friendliness, demonstrating great application potential for large-scale energy storage. However, their cathodic capacity is fundamentally limited by the low solubility of ferricyanide active species. Most previous works merely verified the reversible redox reaction between Prussian blue (PB) and ferrocyanide in symmetric single-electrolyte cells, without systematic quantitative research on solid-liquid matching mechanisms and practical full-cell performance evaluation in iron-sulfur systems. This study explores cathode capacity enhancement and full-cell electrochemical characterization to solve the above bottleneck. Nickel sulfide modified graphite felts were synthesized via an in-situ hydrothermal route, and a redox-targeted symmetric cell was assembled with ferricyanide mediators and solid PB. CV results reveal favorable potential matching, while XRD measurements confirm the reversible phase transition between PB and Prussian white (PW) during cycling. The 0.3 M ferricyanide electrolyte achieves effective PB activation, and among 10–40% addition ratios, the 20% PB loading delivers the optimal capacity increment and material utilization, yielding a maximum discharge capacity of 69.66 mAh and a peak power density of 14.58 mW cm−2 in full-cell tests. Integrating 20% PB into full cells remarkably elevates coulombic, voltage and energy efficiencies, with voltage efficiency improved most prominently. Energy efficiency drops continuously as current density rises from 20 to 60 mA·cm−2. The battery reaches its maximum energy efficiency at 40 °C, since mild heating accelerates solid-liquid redox targeting kinetics without inducing PB lattice distortion or ferrocyanide hydrolysis.

Solar redox flow batteries (SRFBs) provide a promising platform for directly coupling solar energy conversion with electrochemical energy storage, but their performance is still limited by insufficient solar-spectrum utilization and sluggish interfacial charge transfer at photoelectrodes. Herein, an Er-modified TiO2−g-C3N4 heterojunction photoanode was constructed by growing Er-doped TiO2 nanorod arrays on fluorine-doped tin oxide followed by g-C3N4 deposition, and was evaluated in a TEMPO/VCl3-based SRFB. Structural and spectroscopic characterizations show that Er modification preserves the main TiO2 framework, promotes a nanorod-based heterostructure with intimate interfacial contact, and redistributes the optical response toward the visible−near-infrared region. Among the investigated electrodes, the 3 wt % Er:TiO2−g-C3N4 photoanode exhibits the most favorable photoelectrochemical behavior, with the charge-transfer resistance decreasing from 28.55 to 23.82 Ω compared with the undoped TiO2−g-C3N4 electrode. PL/TRPL and TPV measurements further indicate suppressed carrier recombination, with the TPV average lifetime increasing from 27.080 to 107.253 μs after Er modification. Wavelength-dependent IPCE and infrared-filtered photocurrent measurements reveal an enhanced but relatively weak long-wavelength photoresponse, suggesting that Er-related long-wavelength utilization acts as an auxiliary contribution rather than the sole origin of the improved performance. When assembled into a full SRFB, the optimized photoanode delivers stable unbiased photocharging currents of approximately 1.0−1.15 mA cm−2 over repeated cycles, together with a solar-to-chemical conversion efficiency of about 1.15% and an estimated solar-to-output energy efficiency of 0.46−0.50%. Post-cycling SEM and XRD results further support the short-term structural stability of the photoanode. These results demonstrate that optimized Er modification primarily enhances interfacial charge separation and transfer in TiO2−g-C3N4 photoanodes while providing an additional route for long-wavelength photon utilization in integrated solar conversion−storage systems.

Deep eutectic solvents (DESs) are promising electrolyte media for solar redox flow batteries, but their high viscosity and sluggish ion transport can limit redox-species diffusion, interfacial charge transfer, and photocharging performance. This study aimed to regulate a TEMPO/VCl₃-based DES electrolyte by controlled water addition for a Yb,Er-doped TiO₂–g-C₃N₄ photoanode solar redox flow battery. DES electrolytes containing 0, 5, 10, and 15 wt% added water were evaluated by physicochemical, electrochemical, and photoelectrochemical measurements, while full-cell tests compared pristine DES with the half-cell-selected 10 wt% electrolyte. While water incorporation systematically enhanced bulk redox-species transport, the optimal photoelectrochemical performance was achieved at 10 wt% water, rather than 15 wt%. Although the 15 wt% electrolyte exhibited the highest bulk diffusivity, the 10 wt% composition provided the most favorable balance between mass transport and interfacial charge transfer kinetics. The Raman spectra supported water-induced reorganization of the bulk DES hydrogen-bonding network. Full-cell tests confirmed that the 10 wt% water-containing electrolyte delivered higher and more stable photocharging responses than pristine DES over 20 cycles. These results indicate that moderate water regulation is an effective strategy for improving DES-based solar redox flow batteries.

The low redox potentials (vs. SHE) of many organic catholytes restrict the operating voltages of aqueous organic redox flow batteries (AORFBs). Herein, ion-pair and solvation engineering of 4-nitrophenethylamine hydrobromide (4-NPEA·HBr), a commercially available pharmaceutical intermediate, is used to realize a high-potential aqueous organic catholyte (1.24 V vs. SHE) with favorable transport characteristics. In 1 M HCl, the nitro to hydroxylamine proton-coupled electron transfer operates at 1.24 V vs. SHE with fast interfacial kinetics and an apparent diffusion coefficient on the order of 10⁻⁵ cm² s⁻¹. Spectroscopy and multi-scale simulations (DFT, MD, COMSOL) show that bromide forms dynamic solvent-separated ion pairs with the protonated amine, producing a more flexible solvation environment that enables faster molecular transport. In contrast, the chloride salt forms tighter interactions and displays a simulated diffusion coefficient nearly an order of magnitude lower. Flow-cell tests with 4-NPEA·HBr achieve a peak power density of 69.5 mW cm⁻² at 140 mA cm⁻², voltage efficiency above 95 percent between 5 and 60 mA cm⁻², and stable cycling for more than 100 cycles at 20 mA cm⁻² with coulombic efficiency above 85%. Coupling 4-NPEA·HBr with a zinc anode yields a full-cell battery with a ca. 1.65 V discharge plateau and energy efficiency around 78%. These results establish ion-pair and solvation engineering of low-cost nitrophenethylamine salts as an effective strategy to create high-potential, transport-favorable organic catholytes for aqueous flow batteries.