Developing highly efficient electrocatalysts with hierarchical structures while revealing their electrochemical reaction mechanism is crucial for pushing commercial water splitting applications. Herein, a V-doping triggered self-assembly strategy is reported to synthesize dendritic V-Ni3S2@NiO core–shell nanoarrays on nickel foam (V-Ni3S2@NiO/NF), which consist of an ultrathin V-doped NiO nanoshell (2–7 nm) and high-crystalline Ni3S2 core. The unique hierarchical structure offers multidimensional mass and charge transport channels and plentiful catalytically active sites for water splitting reactions, resulting in improved water electrolysis kinetics. More importantly, benefiting from the rapid anodic oxidation and evolution process due to the partial leaching of vanadium(IV) in the V-Ni3S2@NiO/NF material, the highly active amorphous NiOOH phase is immediately generated on the surface of V-Ni3S2@NiO/NF (V-Ni3S2@NiO/NiOOH/NF), which contributes to enhancing the adsorption of OH– and exposing abundant unsaturated active sites and thus remarkably enhanced oxygen evolution reaction (OER) kinetics in basic electrolyte. Moreover, an alkaline electrolyzer assembled by V-Ni3S2@NiO/NF simultaneously functioning as both anode and cathode only needs an extremely small voltage of 1.52 V to yield 10 mA cm–2 and retains this activity for over 55 h. This work provides a new train of thought and tactics for the development of high-efficiency electrocatalysts for overall water splitting.
It remains great challenge to develop precious‐metal‐free electrocatalysts to implement high‐activity electrochemical conversion of O2 into value‐added hydroperoxide species (HO2−), which are vulnerable when exposed to various transition‐metal‐based catalysts. A strategy based on steric hindrance and layered nickel‐based layered double hydroxide (Ni‐LDH) induction has been developed for one‐pot inlaying high‐density ultrathin 2 D Ni‐LDH chips on in situ‐grown carbon nanosheets (Ni‐LDH C/CNSs). The resulting material exhibits high electrocatalytic selectivity with a faradaic efficiency up to 95 % for oxygen reduction into peroxide and attains a fairly high mass activity of approximately 22.2 A g−1, outperforming most metal‐based catalysts reported previously. Systematic studies demonstrate that the greatly increased defect concentration at Ni edge sites of Ni‐LDH chips results in more active sites, which contributes a favorable thermodynamically neutral adsorption of OOH* and adsorbed H2O2 molecules relatively weakly. Additionally, the modified CNSs effectively suppress H2O2 decomposition and avoid O−O bond cleavage to produce H2O by steric effects. The synergistic effect of CNSs and Ni‐LDH chips therefore leads to high activity and high selectivity in a two‐electron pathway. A proof‐of‐concept zinc–air fuel cell is proposed and set up to demonstrate the feasibility of green synthesis of peroxide, generating an impressive H2O2 production rate of 5239.67 mmol h−1 gcat.−1.
Amorphous catalysts, thanks to their uniquely coordinated unsaturated properties and abundance of defect sites, tend to possess higher activity and selectivity than their crystalline counterparts. In this work, we report a facile and general solventcontrolled precipitation method to prepare hybrids of graphene oxide (GO) supporting amorphous metal hydroxide [A-M(OH) x /GO, M = Cu, Co, and Mn], which provides us with tangible materials to study the structure-performance relationship of various amorphous oxides. The systematic investigation of A-Cu(OH) 2 /GO by coupling ex situ/in situ characteristic techniques with electrochemical studies reveals that electrocatalytic activity and selectivity toward a two-electron oxygen reduction reaction (ORR) is highly dependent on the coordinated Cu catalytic sites and the disordered structure of A-Cu(OH) 2 . In situ X-ray absorption near-edge structure (XANES) and density functional theory (DFT) calculation verify that the degree of OH* poisoning (ΔG 0 OH* ) tuned by three-OH-coordinated Cu sites in amorphous structures plays a crucial role in selective catalysis of ORR for H 2 O 2 production. The optimized A-Cu(OH) 2 /GO shows superior activity and high selectivity (~95%) toward H 2 O 2 , as demonstrated by a zinc-air battery capable of on-site H 2 O 2 production with a rate as high as 3401.5 mmol h −1 g −1 .
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