The effects of manifold flow on mass transport in electrochemical filter-press reactors

Redox flow batteries as energy storage systems: materials, viability, and industrial applications

The rapid development and implementation of large-scale energy storage systems represents a critical response to the increasing integration of intermittent renewable energy sources, such as solar and wind, into the global energy grid. Redox flow batteries (RFBs) have emerged as a promising solution for large-scale energy storage due to their inherent advantages, including modularity, scalability, and the decoupling of energy capacity from power output. These attributes make RFBs particularly well-suited for addressing the challenges of fluctuating renewable energy sources. Several redox couples have been investigated for use in RFBs, some of which have already achieved commercialization. However, advancement in RFBs technology faces significant hurdles spanning scientific, engineering, and economic domains. Key challenges include limited energy density, high overall costs, electrolyte instability, and issues related to solvent migration across cation exchange membranes, leading to cross-contamination between anolyte and catholyte. Additionally, anion exchange membranes introduce reverse flow complications, and graphite felt used in the catholyte compartment is susceptible to corrosion. These issues necessitate ongoing research to develop viable solutions. This comprehensive review provides an in-depth analysis of recent progress in electrolyte technologies, highlighting improvements in electrochemical performance, stability, and durability, as well as strategies to enhance the energy and power densities of RFBs. Moreover, it classifies various three-dimensional (3D) electrode materials, including foam, biomass, and electrospun fibers, and examines how their structural and compositional modifications can facilitate improved mass transport and increase active sites for redox reactions in vanadium redox flow batteries (VRFBs). By exploring innovative electrode designs and functional enhancements, this review seeks to advance the conceptualization and practical application of 3D electrodes to optimize RFB performance for large-scale energy storage solutions.

Design, Validation, and Fabrication of a Tailored Electrochemical Reactor Using 3D Printing for Studies of Commercial Boron-Doped Diamond Electrodes

Boron-doped diamond (BDD) electrodes are the most effective and resistant electrodic materials to perform advanced oxidation processes. Having a reactor that can provide adequate hydrodynamic conditions is mandatory to use these electrodes effectively. In this work, the diamond anode electrochemical reactor (E3L-DAER) is designed to fulfill this necessity. Several features are included to improve its efficiency, like conic inlet/outlet, flow enhancers, and a reduced interelectrode gap. The fluid dynamic validation has been performed using computer fluid dynamics (CFD) calculations, residence time distribution (RDT) curves, and mass transfer analysis. The reactor has been made using a three-dimensional (3D) printing stereolithography (SLA) technique, which allows us to build chemical-resistant reactors with nonstandard and tailored features in a cheap and fast way. The obtained results demonstrate that the designed reactor has the required fluid dynamics properties to perform reliable BDD electrode studies and applications. Finally, a BDD electrode was used to test the production of different oxidants such as persulfate, peroxophosphate, and chlorine-derived species.

Clean H2 Production by Lignin-Assisted Electrolysis in a Polymer Electrolyte Membrane Flow Reactor

Biomass-derived products, such as lignin, are interesting resources for energetic purposes. Lignin is a natural polymer that, when added to the anode of an alkaline exchange membrane water electrolyser, enhances H₂ production rates and efficiencies due to the substitution of the oxygen evolution reaction. Higher efficiencies are reported when different catalytic materials are employed for constructing the lignin anolyte, demonstrating that lower catalytic loadings for the anode improves the H₂ production when compared to higher loadings. Furthermore, when a potential of -1.8 V is applied, higher gains are obtained than when -2.3 V is applied. An increase of 200% of H₂ flow rates with respect to water electrolysis is reported when commercial lignin is used coupled with Pt-Ru at 0.09 mg cm^-2 and E = -1.8 V is applied at the cathode. This article provides deep information about the oxidation process, as well as an optimisation of the method of the lignin electro-oxidation in a flow-reactor as a pre-step for an industrial implementation.

Electrogeneration of Active Chlorine in a Filter-Press-Type Reactor Using a New Sb2O5 Doped Ti/RuO2-ZrO2 Electrode: Indirect Indigoid Dye Oxidation

This paper presents the study on active chlorine mediated electrochemical oxidation of model solutions that simulate textile effluents containing an indigoid dye (indigo carmine) and sodium chloride (0.05 M) using a new Sb2O5-doped Ti/RuO2-ZrO2 electrode. The study was carried out in a filter-press electrochemical reactor specially designed to minimize flow deviations and provide homogeneous mass transfer flux over the electrode surface. Firstly, the mass-transfer-limited chloride oxidation reaction was studied in the absence of dye in order to understand the active chlorine formation process. Changes in pH, chloride concentration and UV-visible absorption spectra during electrolysis reveal the formation of active chlorine (mainly hypochlorite) with current efficiencies for chloride oxidation of 0.558 and 0.503 at 10 and 20 mA cm−2, respectively. Secondly, chloride oxidation was investigated in the presence of indigo carmine dye (0.5 mM) where in-situ generated active chlorine was responsible for -C=C- bond breaking and dye degradation. The solution discoloration followed a pseudo-first order kinetics where kinetic coefficient was inversely proportional to dye concentration. The oxidation with active chlorine had an average efficiency of 0.7 and a very competitive energy consumption between 49.2 and 128.5 kW h (kg COD removed)−1 depending on current density and flow rate.