Bipolar Membranes to Promote Formation of Tight Ice‐Like Water for Efficient and Sustainable Water Splitting

Abstract

Bipolar membranes (BPMs) have recently received much attention for their potential to improve the water dissociation reaction (WDR) at their junction by utilizing catalysts. Herein, composite catalysts (Fe2O3@GO) comprising hematite nanoparticles (α‐Fe2O3) grown on 2D graphene oxide (GO) nanosheets are reported, which show unprecedentedly high water dissociation performance in the BPM. Furthermore, new catalytic roles in facilitating WDR at the catalyst–water interface are mechanistically elucidated. It is demonstrated that the partially dissociated bound water, formed by the strongly Lewis‐acidic Fe atoms of the Fe2O3@GO catalyst, helps the “ice‐like water” to become tighter, consequently resulting in weaker intramolecular OH bonds, which reduces activation barriers and thus significantly improves the WDR rate. Notably, Fe2O3@GO‐incorporated BPM shows an extremely low water dissociation potential (0.89 V), compared to commercially available BPM (BP‐1E, 1.13 V) at 100 mA cm−2, and it is quite close to the theoretical potential required for WDR (0.83 V). This performance reduces the required electrical energy consumption for water splitting by ≈40%, as compared to monopolar (Nafion 212 and Selemion AMV) membranes. These results can provide a new approach for the development of water dissociation catalysts and BPMs for realizing highly efficient water splitting systems.

Continuous ammonia electrosynthesis using physically interlocked bipolar membrane at 1000 mA cm−2

“…In order to correlate the relationship among interfacial structure, WD reaction rate, and ionic transportation kinetics of BMs, electrochemical impedance spectroscopy (EIS) measurements were conducted (Supplementary Fig. 20) 30,35,36 and an equivalent circuit containing three serial parts was employed to outline the WD process (Fig. 3g).…”

“…The performance of MBM is further compared with BMs commercial-available or recently reported based on the transmembrane voltage drop at 100 mA cm −2 (U100) and the 1st limiting current density (Fig. 4f and Supplementary Table 1) 18,23,30,32,35,[39][40][41][42][43][44][45][46][47] . Contributed by mortise-tenon joint design, MBM simultaneously represents superiorities in both aspects, anticipating satisfying performances for the novel BM electro reactors that unachieved before.…”

“…Co 3D nanoarray (Supplementary Figs. [29][30][31][32][33][34][35] and the as-prepared NiFe foam 48 were adopted to be cathodic and anodic catalysts. The effective working area for both anode and cathode electrodes is 3.0 cm 2 , respectively, sandwiching a bipolar membrane slightly larger to avoid electrolytes convection on both sides.…”

Bipolar Membrane and Interface Materials for Electrochemical Energy Systems

“…Some of the most commonly used catalysts include inorganic materials (like metal hydroxides , or graphene oxides , and heavy metal ion complexes like those of iron, chromium, and zirconium , ). In particular, GO-based materials have acquired a huge interest due to their high CSD, where the carboxylate groups exhibited the highest reactivity toward the water dissociation. − Water dissociation on the metal oxides and hydroxides is activated by the adsorption of water onto the surface followed by proton transfer from the water to the adjacent oxygen atom, resulting in hydroxide ions. A clear elucidation of the metal oxide surface species and utilization efficiency of metal oxide material helps to identify catalytically active species during water dissociation and the associated electric field impact in the BPM IL.…”

Tuning the Interfacial Electrical Field of Bipolar Membranes with Temperature and Electrolyte Concentration for Enhanced Water Dissociation

“…The bipolar membrane (BPM), comprising a cation exchange layer (CEL) and an anion exchange layer (AEL), has emerged as a promising separator in electrochemical energy conversion and storage devices due to its ability to (i) maintain the target pH conditions for performing the desired electrochemical reactions on both cathode and anode sides, (ii) to avoid ohmic voltage loss increase across the membrane at a high current density as a result of the constant H + and OH – addition attributed to water dissociation at the CEL/AEL interface, and (iii) to effectively block species crossover, e.g., reduced CO 2 crossover in CO 2 electrolytes, to enhance the CO 2 utilization efficiency. − A commonly accepted water dissociation enhancement at the CEL/AEL interface under reverse polarization was induced by two pathways, i.e., electric field enhancement (second Wien effect) and catalytical enhancement due to functional water dissociation catalysts. Various reports have been published on engineering the interface for a larger interfacial electrical field − and searching for higher-performing water dissociation catalysts to reduce the membrane voltage drop. − As the water dissociation reaction takes place primarily at the CEL/AEL interface, a fundamental understanding of the water dissociation mechanism as well as related transport phenomena is crucial for the optimization and design of BPMs. Modeling efforts have been reported to study the interfacial water dissociation kinetics with Onsager’s theory .…”