A facile and effective one‐step in‐situ technique for the synthesis of layered two‐dimensional metallic vanadium sulfide‐reduced graphene oxide (VS2/rGO) nanocomposite (NComp) hasbeen described and their electrocatalytic properties towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been studied. From transmission and scanning electron microscopy analyses, it was observed that the layered two‐dimensional VS2 nanoparticles successfully grew over the layered graphene matrix. The as‐synthesized NComp displayed excellent electrocatalytic activities towards ORR with a four‐electron transfer pathway, and OER in alkaline medium. The synthesized nanocatalyst exhibits lower ΔE value (0.75 V) as compared to other literature values, high catalytic current density (−6.26 mA cm−2 for ORR) with a lower Tafel slope (59 mV dec−1), as compared to Pt/C, and lower overpotential (η=0.31 V at 10 mA cm−2 for OER) with a smaller Tafel slope (68 mV dec−1) than those of RuO2. Moreover, it displays high electrochemically active surface area, long‐term stability in alkaline medium and good resistance to the methanol crossover effect. The enhanced bifunctional electrocatalytic properties of the synthesized nanocatalyst may be owing to the synergistic effect of combining VS2 and rGO, which improves the surface area, adsorption of reaction intermediates, active sites density, and electrical conductivity. Along with the high stability of the hybrid NComp, these advantages provide immense promise for triggering breakthroughs in fuel‐cell electrocatalysis.

Exploring a sustainable, cost-effective, and efficient bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very significant as well as challenging to develop an energy conversion–storage system. Herein, we demonstrate a fabrication technique of an organic–inorganic hybrid polypyrrole (ppy)/AgVO3, and its surface was further modified by porphrin (porphy) to boost its catalytic performances. The C,N-based ppy/AgVO3/porphy nanocatalyst acts as a charge transport highway to accelerate the sluggish OER/ORR kinetics and results in its impressive bifunctional performances. It exhibits an outstanding four-electron ORR activity with higher onset potential (1.03 V) and remarkable OER catalytic performance carrying a lowest overpotential (η10) of 220 mV, largely outperformingAgVO3 and ppy/AgVO3. Initially the very low ORR/OER activities of AgVO3 nanorods come from poor O2 and OH– adsorption on V5+ sites due to its extremely low electrochemical active surface area (ECSA) and poor electrical conductivity. The ppy loading has improved its catalytic performances by providing new active sites due to the presence of pyrrolic-N. Finally, the active site density was greatly enhanced after porphy loading over ppy/AgVO3, as porphy offers additional pyridinic-N along with pyrrolic-N atom. Furthermore, developed mesoporous surface after porpy incorporation provides high electrical conductivity, large surface area, enhanced charge–mass transport, close electrolyte–catalyst contact, and improved stability. Considering its bifunctional activity, NComp has been further evaluated by integrating it into a prototype zinc–air battery (ZAB), where a low discharge–charge voltage gap (0.71 V at 10 mA·cm–2) and a large peak power density (301 mW·cm–2) were achieved. Moreover, the NComp-based rechargeable ZAB (RZAB) is efficient enough to be operated evenly for 100 discharge–charge cycles. Most importantly, our findings may offer a powerful yet easy fabrication method of corrosion resistant high-performance catalyst through regulating active sites for investigating catalysis.

The adverse effects of the advancement of civilization have upset the environment significantly by heavy metal ion toxicity, empoisoning of soil, water, food, etc. In this work, Ag loaded metal...

As an extremely attractive technology for the efficient generation of O 2 and H 2 , water electrolysis involving oxygen and hydrogen evolution reactions (OER, HER) mainly depends on efficient and affordable electrocatalysts. In this work, we initially synthesize silver permanganate, AgMnO 4 (AMO), nanoparticles (NPs) with Pd 0 through NaBH 4 reduction. Subsequently, their surface is further modified using PdO x (x = 1, 1.5, 2) via annealing the AMO/Pd nanocomposite (NComp-1). For the optimization of catalytic properties, the chemical state of oxidic Pd δ+ is modulated by changing the annealing temperature from 160 to 360 °C. The electrocatalytic activity of NComp-1 is observed to improve gradually on increasing the temperature, and it reaches a maximum at 260 °C. This increase in temperature leads to an increase in the chemical state of Pd δ+ species produced at the AMO−Pd interface. Moreover, a temperature of 260 °C provides mixed-valence Pd (0, 2+, 3+), which strongly contributes to excellent OER/HER activities of AMO/PdO x /Pd-260 NComp (NComp-3). However, a temperature of 360 °C converts all Pd to Pd 4+ , which in turn decreases its activity, implying the intrinsic benefit of mixed-valence Pd δ+ toward OER/HER. The optimized NComp-3 features enhanced bifunctional properties, exhibiting extremely low overpotentials (η 10 ) (160 mV for OER, 58 mV for HER at 10 mA cm −2 ) with small Tafel slopes (64.9 mV dec −1 for OER, 37.8 mV dec −1 for HER). Inspired by the superior bifunctionality, a symmetric alkaline electrolyzer is assembled with NComp-3, which needs only 1.50 V to reach a water-splitting current of 10 mA cm −2 and exhibits remarkable long-term stability. The enhanced electrocatalytic performance may be due to the synergetic effect among AMO, PdO x , and Pd, which distinctively improves the adsorption of reaction intermediates, surface area, electrical conductivity, charge-mass transport, and also stability. Therefore, our work highlights the importance of surface engineering through regulating the surface electronic status and also offers a feasible strategy for synthesizing efficient bifunctional electrocatalysts for renewable energy applications.