An oxygen vacancy-modulated bifunctional S-NiMoO4 electrocatalyst for efficient alkaline overall water splitting.

S-doped nickel molybdate nanorods grown on nickel foam (S-NiMoO4/NF) were fabricated by a two-step hydrothermal method. The resultant S-NiMoO4/NF exhibited remarkable bifunctional electrocatalytic activity, with overpotentials of 235 mV for the hydrogen evolution reaction and 150 mV for the oxygen evolution reaction at a current density of 50 mA cm-2. Assembled into the two-electrode S-NiMoO4/NF electrolyzer in alkaline electrolytes for overall water splitting, it required only low cell voltages of 1.55 V and 1.63 V to drive 50 mA cm-2 and 100 mA cm-2, respectively. No significant performance degradation occurred during the water electrolysis process. The experimental results confirmed that S-doping induced the increase of the oxygen vacancies, accelerating the reaction kinetics and thus improving the electrocatalytic performance. Meanwhile, more active sites exposure on the surface of S-NiMoO4/NF enhanced the reactivity. This work may guide the development of efficient bifunctional catalysts in alkaline electrolysis through oxygen vacancy regulation.

N, S codoped carbon matrix-encapsulated CoFe/Co0.2Fe0.8S heterostructure as a highly efficient and durable bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries.

The realization of durable and efficient oxygen evolution reactions (OER) at large current densities and low overpotentials is of significant importance but remains a great challenge. In this study, a CoFe/Co0.2Fe0.8S@NS-CNTs/CC (CF/CFS@NS-CNTs/CC) heterogeneous structure was fabricated by isolating CoFe/Co0.2Fe0.8S (CF/CFS) particles locked in nitrogen/sulfur codoped carbon nanotubes (NS-CNTs). Appreciable oxygen evolution reaction activity and durability was achieved with an ultralow overpotential of 110 mV at 10 mA•cm-2. The operation was stable for 300 h at a current density of 500 mA•cm-2. The structure was then assembled into a zinc-air battery (ZAB), which delivered a high power density of 194 mW•cm-2, a specific capacity of 837.3 mAh•gZn-1, and stable operation for 788 h without obvious voltage attenuation and altered morphology. The electronic interactions were studied by X-ray photoelectron spectroscopy (XPS), which revealed that both the bimetal components and the synergistic effect at the interface stimulated the transfer of Co and Fe sites to higher chemical valence states. Theoretical calculations indicated that the synergistic effect of the bimetal components, build-in interfacial potential, and surface chemical reconstruction adjusted the Fermi level to optimize the thermodynamic formation of O* to OOH*, thus enhancing the intrinsic activity.

Toward the Long-Term Stability of Cobalt Benzoate Confined Highly Dispersed PtCo Alloy Supported on a Nitrogen-Doped Carbon Nanosheet/Fe3C Nanoparticle Hybrid as a Multifunctional Catalyst for Zinc-Air Batteries.

This work reports a new type of platinum-based heterostructural electrode catalyst that highly dispersed PtCo alloy nanoparticles (NPs) confined in cobalt benzoate (Co-BA) nanowires are supported on a nitrogen-doped ultra-thin carbon nanosheet/Fe3C hybrid (PtCo@Co-BA-Fe3C/NC) to show high electrochemical activity and long-term stability. One-dimensional Co-BA nanowires could alleviate the shedding and agglomeration of PtCo alloy NPs during the reaction so as to achieve satisfactory long-term durability. Moreover, the synergistic effect at the interface optimizes the surface electronic structure and prominently accelerates the electrochemical kinetics. The oxygen reduction reaction half-wave potential is 0.923 V, and the oxygen evolution reaction under the condition of 10 mA•cm-2 is 1.48 V. Higher power density (263.12 mW•cm-2), narrowed voltage gap (0.49 V), and specific capacity (808.5 mAh•g-1) for PtCo@Co-BA-Fe3C/NC in Zn-air batteries are achieved with long-term cycling measurements over 776 h, which is obviously better than the Pt/C + RuO2 catalyst. The interfacial electronic interaction of PtCo@Co-BA-Fe3C/NC is investigated, which can accelerate electron transfer from Fe to Pt. Density functional theory calculations also indicate that the interfacial potential regulates the binding energies of the intermediates to achieve the best performance.

Photoelectrocatalytic peroxymonosulfate activation over CoFe2O4-BiVO4 photoanode for environmental purification: Unveiling of multi-active sites, interfacial engineering and degradation pathways.

This work reported on the development of CoFe2O4-BiVO4 photoanode based photoelectrocatalytic system collaborating with peroxymonosulfate activation for organic contaminants removal. CoFe2O4 layer not only provided active sites for direct peroxymonosulfate activation but also accelerated charge separation process for the enhancement of photocurrent density and photoelectrocatalytic performance. Junction of CoFe2O4 layer on BiVO4 photoanode led to the improvement of photocurrent density to 4.43 mA/cm2 at 1.23 VRHE, which was approximately 4.06 times higher than that of pure BiVO4. Subsequently, the corresponding optimal degradation efficiency toward the tetracycline model contaminant achieved to be 89.1% with total organic carbon removal value of about 43.7% within 60 min. Moreover, the degradation rate constant of CoFe2O4-BiVO4 photoanode in photoelectrocatalytic system was 0.037 min-1, which was about 1.23, 2.64 and 3.70 times higher than the values in photocatalysis, electrocatalysis and PMS only based systems, respectively. In addition, radical scavenging experiments and electron spin resonance spectra indicated a synergy of radical and nonradical coupling process where •OH and 1O2 played vital roles during tetracycline degradation. Plausible photoelectrocatalytic mechanism and degradation pathway were proposed. This work provided an effective strategy to construct peroxymonosulfate assisted photoelectrocatalytic system toward green environmental applications.