Vijay Ramani

Efficient electrochemical flow reactors require thin, conductive, and durable flow field plates (FFPs). Graphitic bipolar plates (GBPs) are commonly used as FFPs due to their high conductivity; conductive polymer composites (CPCs) are a promising alternative due to their higher durability and ability to be produced thinner than GBPs. The present study investigates the effect of the morphology of major and minor carbonaceous fillers on CPC properties. As major fillers, high-aspect ratio (high-AR) carbon nanofibers exhibit a lower percolation threshold (1–3 v/v% vs ∼25 v/v%) and produce more conductive and stronger CPCs than 2-D graphite flakes. For minor fillers, nanosized and high-AR particles are optimal to improve CPC properties. minor fillers with diameters of ∼100 nm were found to enhance electrical and mechanical properties more effectively than ∼10 nm diameter fillers. Yet, excessive loadings of minor fillers (>2 v/v%) lead to the emergence of cavities, weakening the CPC properties. Thin CPCs (∼0.9 mm) were developed with lower area-specific resistance (17.6–22.1 vs 26.2 mΩ·cm ² ) than GBPs (3.175 mm) and excellent chemical stability (retaining electrical conductivity over a week in 0.9 M cerium (III/IV) in 2 M methanesulfonic acid). The enhanced properties of CPCs promote their use as FFPs.

Cerium-based redox flow batteries (RFBs) are candidates for large-scale energy storage applications. However, they are hindered by the sluggish kinetics of the cerium redox reaction (Ce³⁺/Ce⁴⁺) and the difficulty of enhancing these kinetics. In this study, we propose a tungsten oxide (WO_3-x)/carbon paper (CP) electrode, fabricated via the atomic layer deposition (ALD) method, which can enhance the cerium redox reaction kinetics and reversibility.

Competition between the chloride oxidation reaction (COR) and oxygen evolution reaction (OER) in brine electrolysis is inherent in the chlor-alkali process and in seawater electrolysis for hydrogen production. The electrocatalytic selectivity for this competition is commonly measured with UV-vis spectroscopy using the N,N-diethyl-p-phenylenediamine (DPD) reagent.[1] While accurate, this method is ex-situ and time consuming. Differential electrochemical mass spectrometry provides an in-situ option but has high equipment costs and specialized cell requirements. An operando alternative, the rotating ring-disk electrode (RRDE), has been studied in low-current density, low-concentration acidic brine [2] as well as low-current density neutral and alkaline brine. [3] The principle of RRDE analysis is to hold a catalyst-coated disk working electrode at oxidizing potentials (E>1.23 V_RHE) where both OER and COR can happen, while holding the Pt-ring at a lower potential where chloride oxidation species reduction reaction (COSRR) occurs but oxygen reduction reaction (ORR) does not. In other words, a ring potential that will measure current which can be exclusively attributed to the reduction of evolved chlorine. This allows for the determination of COR selectivity.

Our supersaturated, phase-change electrolyte paradigm overcomes the energy density limits of redox flow batteries (RFBs) imposed by the solubility of the active species, demonstrating a new strategy for high-energy-density RFBs.

A titanium–cerium redox flow battery (Ti–Ce RFB) operated at 150 mA cm ⁻² with 70% energy efficiency over 80 h and 100 cycles.

Enhancing the catalytic stability of Fe-N-C catalysts for cathodic oxygen reduction in proton-exchange membrane fuel cells (PEMFCs) necessitates an in-depth understanding of their degradation mechanisms. This study identifies key stressors affecting the stability of Fe-N-C catalysts, specifically acidic environment, oxygen (O₂), and reactive oxygen species (ROS). Through ex situ/operando experiments, we show that the oxidation of local carbon by acidic environment + O₂ + ROS, along with the demetalation of catalytic FeN_xC_y sites by O₂ or O₂ + ROS, is the primary factor responsible for the initial fast degradation of Fe-N-C catalysts. The demetalation of FeN_xC_y sites, influenced by O₂, in particular by O₂ + ROS, leads to the subsequent gradual degradation of Fe-N-C. Notably, FeN₄C₁₂-type active sites are more susceptible to demetalation than FeN₄C₁₀-type sites in O₂ or O₂ + ROS. Our findings indicate that, besides constructing more stable FeN_xC_y sites, preventing local carbon oxidation and scavenging of ROS are all critical for maintaining the stability of Fe-N-C catalysts.

Redox flow batteries (RFBs) are promising, scalable energy storage systems, due to their decoupling of power density and energy capacity. Amongst the many different redox couples considered in RFBs, the cerium redox couple, Ce(IV)/ Ce(III), is particularly attractive due to its high standard potential (1.61 V vs standard hydrogen electrode, SHE) and the relative abundance of Ce in the Earth’s crust (as abundant as lead). However, the practical application of Ce in RFBs is typically limited by the low solubility of Ce ions in electrolyte, limiting the realizable practical energy density. Herein, in a departure from previous studies which utilize acid-supported Ce electrolyte solutions (e.g., with sulfuric acid), we have developed a new Ce electrolyte with ammonium sulfate (AS) working as the supporting electrolyte. The solubility of Ce(IV) was enhanced to 1.23 M by optimizing solution composition. The study of solution chemistry combined with experimental techniques (Raman, UV-Vis) and theoretic calculation based on equilibrium constants revealed that such a supersaturated state is a synthetic effect of Ce(IV) hydrolysis with water and complexation with sulfate. This cost-effective Ce electrolyte was paired with titanium (Ti) redox couples in a RFB to test the capacity and efficiencies, and a reversible cycling behavior was observed.

The direct methanol hydrogen peroxide fuel cell (DMHPFC) with a pH-gradient microscale bipolar interface (PMBI) achieves a high open circuit voltage of 1.69 V and peak power density of 630 mW cm ⁻² by optimising an alkaline anode and acidic cathode.