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Efficient electrochemical overall water splitting requires bi‐functional catalysts that work for both hydrogen and oxygen evolution reactions (HER/OER). A heterostructure is thus proposed to maintain its optimal interactions with H/O‐containing intermediates. A so‐called "orbital occupancy self‐equilibrium" strategy is employed theoretically and experimentally to design such bi‐functional catalysts, namely the incorporation of the V species into a NiS/NiS2 heterostructure. Owing to the variable valences of both Ni and V species, the electrons are controllably reoriented over the interfacial V─S─Ni bond. The as‐generated dynamic and self‐equilibrium of the electron environment modify an optimal adsorption harmony toward various H/O‐containing intermediates on this heterointerface, enhancing intrinsic activity and reaction kinetics for the HER, the OER, and overall water splitting. This V‐NiS/NiS2 catalyst exhibits an overpotential of only 94 and 220 mV at a current density of 10 mV cm–2 for the HER and the OER, respectively. This proposed strategy is expected to be workable for other catalysts with variable metal valences and provide insights for an agile interfacial electron allocation on heterostructure catalysts. [ABSTRACT FROM AUTHOR]

2D MXenes are widely proved to be potential electrode materials, although the size effect on their electrochemistry is not fully understood. In this work, Ti3C2Tx nanoflakes are prepared through acidic etching of Ti3AlC2 powders, followed by the intercalation treatment with tetrapropylammonium hydroxide. Such a method produces large‐scale delaminated and oxygenated nanoflakes. With aid of centrifugation, the nanoflakes with varied lateral sizes and thicknesses are collected, where electrochemical response of charged redox probes and polar phenol molecules is varied. Density functional theory and energy dispersive spectroscopy confirm such electrochemical response is dependent on the size and thickness of used nanoflakes, more exactly the oxygen content on their surface. Taking the nanoflakes obtained using a centrifugal speed of 5000 rpm (MX‐TPA0.2) as an example, they feature good dispersibility, a high oxygen content, a small size, and a thin thickness. On these nanoflakes electrochemical response of polar p‐substituted phenols is pronounced, stemming from a strong electron‐withdrawing interaction of their oxygenated termination with the Ar‐OH. A sensitive electrochemical sensor is further constructed for the detection of p‐nitrophenol. This work thus provides an approach to synthesize MXenes with different sizes and thicknesses as well as further to reveal size‐dependent electrochemistry of MXenes. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous zinc‐ion hybrid capacitors (ZHCs) have aroused unprecedented attention because of their high safety, cost effectiveness, and environmental compatibility. However, the intractable issues of dendrite growth and side reactions at the electrode–electrolyte interface deteriorate durability and reversibility of Zn anodes, deeply encumbering the large‐scale application of ZHCs. Concerning these obstacles, a negatively charged carboxylated chitosan‐intensified hydrogel electrolyte (CGPPHE) with cross‐linked networks is reported to stabilize Zn anodes. Beyond possessing good mechanical characteristics, the CGPPHE with polar groups can reduce the desolvation energy barrier of hydrated Zn2+, constrain the 2D Zn2+ diffusion, and uniformize electric field and Zn2+ flux distributions, assuring dendrite‐free Zn deposition with high plating–stripping efficiency. Concurrently, the hydrophilic CGPPHE alleviates harmful hydrogen evolution and corrosion by abating water activity. Accordingly, Zn|CGPPHE|Zn and Zn|CGPPHE|Cu cells exhibit an extended life exceeding 350 h (1600 mAh cm−2 cumulative capacity under 20 mA cm−2) and a high average coulombic efficiency of 98.2%, respectively. The resultant flexible ZHCs with CGPPHE and template‐regulated carbon cathode present perfect properties in capacity retention (97.7% over 10 000 cycles), energy density (91.8 Wh kg−1), and good mechanical adaptability. This study provides insight into developing novel hydrogel electrolytes toward highly rechargeable and stable ZHCs. [ABSTRACT FROM AUTHOR]

Red phosphorus (RP) is a promising electrochemical sensing material owing to its abundant surface groups and reactive sites. In this study, a sodium dodecyl sulfate‐assisted phosphorus‐amine approach is employed to tune surface chemistry of RP nanoparticles. During the transition of the polyphosphorus‐amine anion to RP, the cleavage of POP bond and the formation of POC bond are monitored by in situ attenuated total reflection surface‐enhanced infrared absorption spectroscopy. The formed POC bonds that are originated from the PO reactive sites are theoretically revealed with the density functional theory calculations, charge density difference, and X‐ray photoelectron spectroscopy. The energies of optimized aromatic and aliphatic POC bonds are −2.51 and −2.65 eV, respectively. To explore electrochemical sensing applications, RP nanoparticles are in situ grown on single‐walled carbon nanotube (SWCNT). Such a stable RP/SWCNT suspension is applied to fabricate the RP/SWCNT integrated arrays via a template‐filtration method. Such an array is efficient for sensitive and selective monitoring of p‐phenylenediamine on hair dyes. This study provides insights into surface chemistry of RP, its roles in electrochemical sensing applications, and an approach to produce high‐performance RP sensors at large scales. [ABSTRACT FROM AUTHOR]

Efficient hydrogen production from electrochemical overall water splitting requires high‐performance electrocatalysts for hydrogen evolution reaction (HER) and a fast oxidation reaction to replace sluggish oxygen evolution reaction. Herein, Co‐doped Rh nanoparticles are thus grown on carbon black using Co nanosheets as the bridge. These nanoparticles with a size of ≈1.94 nm exhibit the overpotential of as low as 2 mV at 10 mA cm−2 for the HER, and a mass activity of as high as 889 mA mg−1 for the methanol oxidation reaction (MOR) in alkaline media. As confirmed by density functional theory simulations, such excellent activity originates from Co‐doping, which reduces reaction energy barriers for both the rate‐determining step of a Volmer process during the HER and the conversion of *CO to COOH* during the MOR (namely the enhanced adsorption of H2O and COOH*). Coupling boosted HER on the cathode with accelerated MOR on the anode, efficient H2 generation is achieved. This two‐electrode cell only requires a cell voltage of 1.545 V at 10 mA cm−2 with impressive long‐life cycling stability. Such performance even outperforms that of commercial Pt/C || IrO2 cell. This study offers a new strategy to achieve efficient HER from overall water splitting. [ABSTRACT FROM AUTHOR]