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Bipolar redox‐active organic molecule (BROM) is a feasible strategy to address the cross‐contamination issue of the electrolyte and, thus, improve the stability of the flow battery. Herein, a highly‐soluble BROM is developed by combining the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and viologen moieties, and extensive characterizations are performed to evaluate its applicability in flow battery. Salient findings are as follows. First, the compound, viz. 1‐(1‐oxyl‐2,2,6,6‐tetramethylpiperidin‐4‐yl)‐1′‐(3‐(trimethylammonio)propyl)‐4,4′‐bipyridinium trichloride ((TPABPy)Cl3), features highly hydrophilic groups and yields a high aqueous solubility of 1.76 m. Second, the electrochemical result reveals that the (TPABPy)Cl3 displays two pairs of highly reversible peaks at −0.56 and 0.76 V, which respectively correspond to the viologen and TEMPO moieties. The electronic structure during the redox reactions is identified by both the density functional theory calculation and the electron paramagnetic resonance. Third, the flow battery fed with the 1.0 m (TPABPy)Cl3 solution delivers a high capacity of 25 Ah L−1 and a superior stability over the non‐bipolar counterparts. More to the point, the capacity decay can be effectively recovered by applying the polarity‐inversion rebalance strategy on the BROM. In summary, this work provides a molecular engineering way to rationally design a BROM to improve the capacity and stability of aqueous organic redox flow batteries. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency of water splitting. In this work, a highly active and stable, meso–macro hierarchical porous Ni3S4 architecture, enriched in Ni3+ is designed as an advanced electrocatalyst for OER. The obtained Ni3S4 architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm−2 and 300 mV at 50 mA cm−2. Additionally, this Ni3S4 catalyst has excellent long‐term stability (no degradation after 300 h at 50 mA cm−2). The outstanding OER performance is due to the high concentration of Ni3+ and the meso–macro hierarchical porous structure. The presence of Ni3+ enhances the chemisorption of OH−, which facilitates electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water‐splitting electrolyzer using the prepared Ni3S4 as the anode catalyst and Pt/C as the cathode catalyst achieves a low cell voltage of 1.51 V at 10 mA cm−2. Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni3+ and hierarchical porous architectures. [ABSTRACT FROM AUTHOR]

The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y2‐xCoxRu2O7−δ results in an ultrahigh OER activity because of the charge redistribution at eg orbitals between Ru and Co atoms. The Y1.75Co0.25Ru2O7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H2SO4 at the current density of 10 mA cm−2, which is smaller than that of parent Y2Ru2O7−δ (360 mV) and commercial RuO2 (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen‐mediated mechanism. [ABSTRACT FROM AUTHOR]

The resource scarcity and high cost seriously hamper the large‐scale application of platinum to catalyze the hydrogen evolution reaction (HER). An extraordinarily efficient single‐layer Pt (SL‐Pt) cluster catalyst is synthesized by a facile photolysis‐electroreduction method. Electron microscopy and atomic force microscopy images demonstrate the single‐layer structure with a thickness of ≈0.3 nm. Density functional theory calculations reveal that the charge is redistributed in the SL‐Pt cluster, which yields a downshift in d‐band center of Pt 5d orbital. The above two features of the SL‐Pt cluster yield a high atomic utilization and superior intrinsic activity when used as the electrocatalyst. As a result, the electrochemical test reveals its mass activity of the HER is two orders of magnitude higher than the commerical Johnson–Matthey 20 wt.% Pt/C. As demonstration, the SL‐Pt cluster exhibits a low electrolysis voltage of ≈1.74 V at 1.0 A cm−2 with superior stability up to 48 h in a single‐cell proton exchange membrane water electrolyzer. This study does not only provide a facile method to prepare single‐layer metal cluster, but also provides a stable HER's catalyst for efficient water splitting. [ABSTRACT FROM AUTHOR]