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Designing efficient and bifunctional electrocatalysts for water splitting conforms to the concept of energy conservation and emission reduction but remains challenging now. Herein, the fabrication of a heterostructure by anchoring cobalt‐polyoxometalates (Co‐POM) on NiFe layered double hydroxide (NiFe‐LDH) nanoplates in situ on nickel foam (NF) is first reported (Co‐POM@LDH/NF). The surface area, electron transfer ability, and stability of the heterostructure are increased due to the synergistic effect between Co‐POM and NiFe‐LDH. Particularly, Co‐POM@LDH/NF can deliver a current density of 100 mA cm−2 with an overpotential of only 220 mV for hydrogen evolution reaction (HER) and 226 mV for oxygen evolution reaction (OER) in 1.0 m KOH electrolytes. Impressively, the outstanding stability of Co‐POMs in heterostructures is verified by the experimental observations after electrolysis, indicating the successful construction of stable POMs‐based heterogeneous electrocatalysts. More attractively, the electrolyzer composed by Co‐POM@LDH/NF as anode and cathode shows a much lower operating voltage of 1.51 V at the current density of 10 mA cm−2 for overall water splitting. This study provides a feasible and extensible idea for the design of the POM‐based heterostructures. [ABSTRACT FROM AUTHOR]

Seawater electrolysis to produce hydrogen is a critical technology in marine energy projects; however, the severe anode corrosion caused by the highly concentrated chloride is a key issue should be addressed. In this work, we discover that the addition of sulfate in electrolyte can effectively retard the corrosion of chloride ions to the anode. We take nickel foam as the example and observe that the addition of sulfate can greatly improve the corrosion resistance, resulting in prolonged operating stability. Theoretical simulations and in situ experiments both demonstrate that sulfate anions can be preferentially adsorbed on anode surface to form a negative charge layer, which repulses the chloride ions away from the anode by electrostatic repulsion. The repulsive effect of the adsorbed sulfate is also applicable in highly‐active catalyst (nickel iron layered double hydroxide) on nickel foam, which shows ca. 5 times stability of that in traditional electrolyte. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) are a family of layer materials that receive heightened attention. Herein a ternary NiFeMn-LDH is investigated with superior oxygen evolution activity, which is attributed to the Mn4+ doping in the intralayer, which modifies the electronic structure and improves the conductivity of the electrocatalyst. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) are a family of high-profile layer materials with tunable metal species and interlayer spacing, and herein the LDHs are first investigated as bifunctional electrocatalysts. It is found that trinary LDH containing nickel, cobalt, and iron (NiCoFe-LDH) shows a reasonable bifunctional performance, while exploiting a preoxidation treatment can significantly enhance both oxygen reduction reaction and oxygen evolution reaction activity. This phenomenon is attributed to the partial conversion of Co2+ to Co3+ state in the preoxidation step, which stimulates the charge transfer to the catalyst surface. The practical application of the optimized material is demonstrated with a small potential hysteresis (800 mV for a reversible current density of 20 mA cm−2) as well as a high stability, exceeding the performances of noble metal catalysts (commercial Pt/C and Ir/C). The combination of the electrochemical metrics and the facile and cost-effective synthesis endows the trinary LDH as a promising bifunctional catalyst for a variety of applications, such as next-generation regenerative fuel cells or metal-air batteries. [ABSTRACT FROM AUTHOR]

The morphology and phase transformation of CoAl layered double hydroxide (denoted CAL) nanoplates are systematically investigated in highly concentrated basic solution. Characterization results reveal that this is a time-dependent process, in which CALs are gradually converted to β-Co(OH)2 and CoOOH, and the structure becomes increasingly porous. This process could be caused by the dissolution of the Al part of CoAl LDHs, recrystallization of the Co part, and subsequent oxidation of Co. It is found that the pseudocapacitive performance of the products vary with the immersion time. CALs already show a reasonable performance, whereas short-term treatment would lead to the enhanced capacitance of 1123 F g−1 with both remarkable rate capability and stability. However, the formation of CoOOH will significantly degrade the supercapacitive performance. [ABSTRACT FROM AUTHOR]

Sulfonamides have attracted special attention due to their widespread use and refractory nature in the aquatic environment. Heterogeneous catalytic peroxymonosulfate (PMS) activation for sulfonamide degradation has been demonstrated to be an encouraging strategy. Herein, ultrathin nickel aluminium layered double hydroxide (U–NiAl-LDH) was employed as an efficient peroxymonosulfate activator. The adsorption kinetics experiment showed that U–NiAl-LDH exhibited a super-adsorption phenomenon for sulfonamide antibiotics, such as sulfamethoxazole (SMX) and sulfachloropyridazine (SCP). U–NiAl-LDH was composed of 6 layers of a NiAl bimetallic layer structure. The degradation performance of organic contaminants via PMS activation was greatly accelerated by decreasing the number of LDH layers. Ni(II) on the surface of U–NiAl-LDH activated PMS to produce surface-bound hydroxyl radicals and sulfate radicals by donating electrons to cleave the O–O bond of PMS. These in-situ generated reactive oxygen species (ROS) on the surface of U–NiAl-LDH could directly attack adjacent adsorbed SMX or SCP molecules, where the migration distance between the ROS and target contaminants was reduced. Consequently, super-adsorption synergistically promoted the degradation efficiency of SMX and SCP, which decreased the demand for PMS. The newly found ultra-adsorption enhancing peroxymonosulfate activation effect was pioneered for the ultrafast elimination of sulfonamide antibiotics in real water. This proposed mechanism provides preliminary guiding significance to design PMS catalysts with dual reaction sites for the treatment of targeted refractory organic contaminant wastewater. Schematic illustration of possible reaction mechanism of the U–NiAl-LDH and PMS system. [Display omitted] • Ultrathin NiAl-LDH was synthesized by formamide-assisted precipitation method. • U–NiAl-LDH exhibited super-adsorption effect for sulfonamide antibiotics. • Strong electron donating capability contributed to the outstanding PMS activation. • Migration distance between reactive oxygen species and contaminants was reduced. • Sulfonamide antibiotics in real water were rapidly and accurately eliminated. [ABSTRACT FROM AUTHOR]