Titanium Nitride Nanorods Array-Decorated Graphite Felt as Highly Efficient Negative Electrode for Iron-Chromium Redox Flow Battery

A silver-bismuth bimetallic functionalized negative electrode for iron-chromium flow batteries

The sluggish redox kinetics of chromium ions at the negative electrode have hindered the development of iron-chromium redox flow batteries. A silver-bismuth bimetallic composite-modified electrode was fabricated via electrodeposition to address this limitation. The modified electrode significantly enhanced the reversibility and electrochemical activity of the Cr3+/Cr2+ redox reaction. Single-cell performance evaluation demonstrated that the modified electrode achieved coulombic, voltage, and energy efficiencies of 95.09%, 82.26%, and 78.22% at 40 mA cm-2, respectively. The energy efficiency is increased by 17% compared to conventional graphite felt electrodes.

Anisotropy Engineering for Constructing Gradient Electrodes with High-Efficiency Bi/C Catalyst In Situ for Iron-Chromium Flow Battery

Iron-chromium flow batteries (ICFBs) are regarded as one of the most potential large-scale energy storage devices. Nevertheless, the slow dynamics of the Cr3+/Cr2+ redox couples hinder the development of ICFBs. Here, a high-efficiency carbon-loaded bismuth (Bi/C) catalyst is fabricated and introduced on the electrode in situ to improve the dynamics with the assistance of polyvinylpyrrolidone (PVP). To derive the greatest value, we explore the current density anisotropy in ICFB and design a strategy of anisotropy engineering to meet the requirements of the anisotropy for catalysts. In the work, the gradient electrode (G-PBiC/TCF) with a high-efficiency Bi/C catalyst is successfully prepared. In addition, the ICFB assembled with the G-PBiC/TCF(M/m, the side of more catalysts facing the Membrane side) shows excellent battery performance. It can run over 500 cycles with EE of 81.36% at 120 mA cm-2, which is the longest cycle life reported. Furthermore, the catalytic mechanism and the effect of the catalyst distribution on the performance are explained by the DFT calculation and multi-physical field simulation. This work provides a novel pathway to design that catalyst-supported gradient electrode with high performance and low cost.

Carbon Felts Uniformly Modified with Bismuth Nanoparticles for Efficient Vanadium Redox Flow Batteries

The integration of intermittent renewable energy sources into the energy supply has driven the need for large-scale energy storage technologies. Vanadium redox flow batteries (VRFBs) are considered promising due to their long lifespan, high safety, and flexible design. However, the graphite felt (GF) electrode, a critical component of VRFBs, faces challenges due to the scarcity of active sites, leading to low electrochemical activity. Herein, we developed a bismuth nanoparticle uniformly modified graphite felt (Bi-GF) electrode using a bismuth oxide-mediated hydrothermal pyrolysis method. The Bi-GF electrode demonstrated significantly improved electrochemical performance, with higher peak current densities and lower charge transfer resistance than those of the pristine GF. VRFBs utilizing Bi-GF electrodes achieved a charge-discharge capacity exceeding 700 mAh at 200 mA/cm2, with a voltage efficiency above 84%, an energy efficiency of 83.05%, and an electrolyte utilization rate exceeding 70%. This work provides new insights into the design and development of efficient electrodes, which is of great significance for improving the efficiency and reducing the cost of VRFBs.

Proton conductive 2D MXene-derived potassium titanate nanoribbons fabricated electrochemical platform for trace detection of enrofloxacin

In recent years, due to exceptional properties like broad interlayered spacing and low working potential, MXene-derived titanate nanoribbons have been established as promising electrode materials. Herein, the electrocatalytic activity of MXene-derived potassium titanate nanoribbon was employed to develop a voltammetric sensor for the detection of enrofloxacin. The sensor's significance is to provide a sustainable solution to quantify the presence of enrofloxacin regarding food safety and environmental monitoring. Moreover, to achieve the United Nations' Sustainable Development Goals by preventing antimicrobial resistance to accomplish the One Health approach. Potassium titanate nanoribbons were synthesized using 2D Ti3C2 MXene as an active precursor material, while X-ray diffraction spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction pattern, elemental mapping, and energy-dispersive X-ray spectroscopy were used to characterize the crystallinity, surface and layered morphology of synthesized nanoribbons. The Brunauer-Emmett-Teller (BET) technique was applied to calculate the specific surface area of the synthesized materials. The materials underwent electrochemical characterization using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Later on, the nanoribbons were fabricated on the surface of a glassy carbon electrode, and the electro-oxidative behaviour of enrofloxacin was studied by CV, DPV, square wave voltammetry (SWV) in 0.1 M phosphate buffer (optimized pH 8). The developed sensor depicts a significantly lower limit of quantification of 0.007 μM (≈2.5 μg/L), and an upper limit of quantification of 18 μM (≈6.5 mg/L) along with a limit of detection (LOD) of 0.00279, 0.00803, 0.00881 μM obtained from CV, DPV, and SWV respectively. Furthermore, the developed electrodes show a reliable selectivity to be examined in real complex matrices, i.e. marine water, river water, agricultural soil, organic fertilizer, milk, honey, and poultry egg.

The design engineering of nanocatalysts for high power redox flow batteries

Redox flow batteries (RFBs) are one of the most promising long-term energy storage technologies which utilize the redox reaction of active species to realize charge and discharge. With the decoupled power and energy components, RFBs exhibit high battery pile construction flexibility and long lifespan. However, the inherent slow electrochemical kinetics of the current widely applied redox active species severely impedes the power output of RFBs. Developing high performance electrocatalysts for these redox active species would boost the power output and energy efficiency of RFBs. Here, we present a critical review of nanoelectrocatalysts to improve the sluggish kinetics of different redox active species, mainly including the chemical components, structure and integration methods. The relationship between the physicochemical properties of nanoelectrocatalysts and the power output of RFBs is highlighted. Finally, the future design of nanoelectrocatalysts for commercial RFBs is proposed.

Reduced graphene oxide/MXene hybrid decorated graphite felt as an effective electrode for vanadium redox flow battery

Vanadium redox flow battery (VRFB) is a highly suitable technology for energy storage and conversion in the application of decoupling energy and power generation. However, the sluggish reaction kinetics of redox couples is one of the bottlenecks hindering the commercialization of VFFBs. Developing efficient electrode is a promising method to improve the battery performance. In this work, a reduced graphene oxide/Mxene hybrid-decorated graphite felt (rGO/Mxene@GF) is designed to facilitate the kinetics of redox reaction. The electrocatalytic activity and mass transfer of the prepared electrode are investigated through experiment and simulation methods. The results indicate that the favorable mass transfer and the synergistic effect between rGO and Ti3C2Tx Mxene remarkably improve the performance of electrode. The flow cell with rGO/Mxene@GF delivers a good stability up to 100 cycles with a coulombic, voltage, and energy efficiency of 91.6%, 82.7%, and 75.8%, respectively, at a current density of 80 mA cm-2. These findings suggest that the as-prepared rGO/Mxene@GF holds a good application potential in VRFB and provides a promising approach to design efficient electrode for electrochemical devices.

Machine learning-enabled performance prediction and optimization for iron-chromium redox flow batteries

Iron-chromium flow batteries (ICRFBs) are regarded as one of the most promising large-scale energy storage devices with broad application prospects in recent years. However, transitioning from laboratory-scale development to industrial-scale deployment can be a time-consuming process due to the multitude of complex factors that impact ICRFB stack performance. Herein, a data-driven optimization methodology applying active learning, informed by an extensive survey of the literature encompassing diverse experimental conditions, is proposed to enable exceptional precision in predicting ICRFB system performance considering both operation conditions and key materials selection. Specifically, multitask ML models are trained on experimental data with a high prediction accuracy (R2 > 0.92) to link ICRFB properties to energy efficiency, coulombic efficiency, and capacity. We also interpret the ML models based on Shapley additive explanations and extract valuable insights into the importance of descriptors. It is noted that the operation conditions (current density and cycle number) and the electrode type are the most critical descriptors affecting the voltage efficiency and coulombic efficiency while the electrode size strongly affects the capacity. Moreover, active learning is used to explore the most optimized cases considering the highest energy efficiency and capacity. The versatility and robustness of the approach are demonstrated by the successful validation between ML prediction and our experiments of energy efficiency (±0.15%) and capacity (±0.8%). This work not only affords fruitful data-driven insight into the property-performance relationship, but also unveils the explainability of critical properties on the performance of ICRFBs, which accelerates the rational design of next-generation ICRFBs.