Hybrid Redox Flow Cells with Enhanced Electrochemical Performance via Binderless and Electrophoretically Deposited Nitrogen-Doped Graphene on Carbon Paper Electrodes

Abstract

Hybrid redox flow cells (HRFC) are key enablers for the development of reliable large-scale energy storage systems; however, their high cost, limited cycle performance, and incompatibilities associated with the commonly used carbon-based electrodes undermine HRFC’s commercial viability. While this is often linked to lack of suitable electrocatalytic materials capable of coping with HRFC electrode processes, the combinatory use of nanocarbon additives and carbon paper electrodes holds new promise. Here, by coupling electrophoretically deposited nitrogen-doped graphene (N-G) with carbon electrodes, their surprisingly beneficial effects on three types of HRFCs, namely, hydrogen/vanadium (RHVFC), hydrogen/manganese (RHMnFC), and polysulfide/air (S-Air), are revealed. RHVFCs offer efficiencies over 70% at a current density of 150 mA cm–2 and an energy density of 45 Wh L–1 at 50 mA cm–2, while RHMnFCs achieve a 30% increase in energy efficiency (at 100 mA cm–2). The S-Air cell records an exchange current density of 4.4 × 10–2 mA cm–2, a 3-fold improvement of kinetics compared to the bare carbon paper electrode. We also present cost of storage at system level compared to the standard all-vanadium redox flow batteries. These figures-of-merit can incentivize the design, optimization, and adoption of high-performance HRFCs for successful grid-scale or renewable energy storage market penetration.

A cost-effective alkaline polysulfide-air redox flow battery enabled by a dual-membrane cell architecture

“…Electrochemical measurements were performed using an Autolab potentiostat/galvanostat (PGSTAT302N, Metrohm). Polarisation measurements of the Ni foams in 1 M Na 2 S 2 + 1 M NaOH electrolyte was conducted using the linear scan voltammetry (LSV) method in the overpotential window of −200–200 mV with a scan rate of 1 mV s −1 as reported earlier 21 . Polarisation curve measurements of the PSA RFB were performed using the chronopotentiometry method, where the anolyte and catholyte used 10 mL 1 M Na 2 S 2 + 1 M NaOH solution and 50 mL 1 M NaOH solution, respectively.…”

“…For these reasons, the organic-solvent-based polysulfide chemistry has been widely looked into in lithium-sulfur batteries and sodium-sulfur batteries 10 , 11 . On the other hand, the aqueous polysulfide redox couple has been adopted in a number of RFB systems, including polysulfide-bromine 12 – 14 , polysulphide-iodide 7 , 15 – 17 , polysulphide-ferrocyanide 18 and polysulfide-air (PSA) 19 – 21 . Among these, the PSA system has the lowest chemical cost of storage due to its use of the inexpensive oxygen redox couple.…”

Application of Nanomaterials in Aqueous Redox Flow Batteries

“…Graphene‐based nanomaterials such as graphene, [46–49] reduced graphene oxide (rGO) [50,51] and graphene oxide [52] have been widely applied in VRFBs attributed to outstanding conductivity, large specific surface area and excellent stability in strong acid solution. Composite electrode of CF with graphene deposited via in‐situ growth showed improved electrocatalytic activity and redox kinetics towards VO 2+ /VO 2 + ascribed to the increased specific surface area of CF and abundant sharp graphene edges [53] .…”

Practical aspects of electrophoretic deposition to produce commercially viable supercapacitor energy storage electrodes

“…and pore size distribution was calculated by QSDFT method using isothermal data as detailed in our recent investigation on redox ow battery. 5,11,12 Pouch cell manufacture and performance testing…”

“…The charged particles migrate to a deposition substrate, then are deposited onto it and form a layer by deposits build-up. Recent years are seeing many published evidence in EPD for energy storage applications; notably lithium-ion battery electrode, 1 solid-state electrolyte, 2 membrane electrode assembly, 3 supercapacitor 4 and flow battery, 5 but their advancement for industrialisation are far from actual adoption. An obvious reason is because the published research have only focused on depositing very thin layer (<1 μm), which gives the extreme performance values that can only be attributed to a complete utilization of low density active materials (1 mg cm −2 ) for fast accessibility of electrons and ions.…”