RESUMEN
Noble metal free electrocatalysts for hydrogen evolution reaction (HER) in acid play an important role in proton exchange membrane-based electrolysis. Here, we develop an in situ surface self-reconstruction strategy to construct excellent acidic HER catalysts. Firstly, free-standing zinc nickel tungstate nanosheets inlaid with nickel tungsten alloy nanoparticles were synthesized on carbon cloth as pre-catalyst via metal-organic framework derived method. Amorphous nickel tungsten oxide (Ni-W-O) layer is in situ formed on surface of nanosheet as actual HER active site with the dissolution of NiW alloy nanoparticles and the leaching of cations. While the morphology of the free-standing structure remains the same, keeping the maximized exposure of active sites and serving as the electron transportation framework. As a result, benefiting from disordered arrangement of atoms and the synergistic effect between Ni and W atoms, the amorphous Ni-W-O layer exhibits an excellent acidic HER activity with only an overpotential of 46 mV to drive a current density of 10 mA cm-2 and a quite good Tafel slope of 36.4 mV dec-1 as well as an excellent durability. This work enlightens the exploration of surface evolution of catalysts during HER in acidic solution and employs it as a strategy for designing acidic HER catalysts.
RESUMEN
Rechargeable zinc-air batteries afford great potential toward next-generation sustainable energy storage. Nevertheless, the oxygen redox reactions at the air cathode are highly sluggish in kinetics to induce poor energy efficiency and limited cycling lifespan. Air cathodes with asymmetric configurations significantly promote the electrocatalytic efficiency of the loaded electrocatalysts, whereas rational synthetic methodology to effectively fabricate asymmetric air cathodes remains insufficient. Herein, a strategy of asymmetric interface preconstruction is proposed to fabricate asymmetric air cathodes for high-performance rechargeable zinc-air batteries. Concretely, the asymmetric interface is preconstructed by introducing immiscible organic-water diphases within the air cathode, at which the electrocatalysts are in situ formed to achieve an asymmetric configuration. The as-fabricated asymmetric air cathodes realize high working rates of 50 mA cm-2 , long cycling stability of 3400 cycles at 10 mA cm-2 , and over 100 cycles under harsh conditions of 25 mA cm-2 and 25 mAh cm-2 . Moreover, the asymmetric interface preconstruction strategy is universal to many electrocatalytic systems and can be easily scaled up. This work provides an effective strategy toward advanced asymmetric air cathodes with high electrocatalytic efficiency and significantly promotes the performance of rechargeable zinc-air batteries.
RESUMEN
Rechargeable zinc-air batteries are considered as next-generation energy storage devices because of their ultrahigh theoretical energy density of 1086â Wh kg-1 (including oxygen) and inherent safety originating from the use of aqueous electrolyte. However, the cathode processes regarding oxygen reduction and evolution are sluggish in terms of kinetics, which severely limit the practical battery performances. Developing high-performance bifunctional oxygen electrocatalysts is of great significance, yet to achieve better bifunctional electrocatalytic reactivity beyond the state-of-the-art noble-metal-based electrocatalysts remains a great challenge. Herein, a composite Co3 O4 @POF (POF=framework porphyrin) bifunctional oxygen electrocatalyst is proposed to construct advanced air cathodes for high-performance rechargeable zinc-air batteries. The as-obtained composite Co3 O4 @POF electrocatalyst exhibits a bifunctional electrocatalytic reactivity of ΔE=0.74â V, which is better than the noble-metal-based Pt/C+Ir/C electrocatalyst and most of the reported bifunctional ORR/OER electrocatalysts. When applied in rechargeable zinc-air batteries, the Co3 O4 @POF cathode exhibits a reduced discharge-charge voltage gap of 1.0â V at 5.0â mA cm-2 , high power density of 222.2â mW cm-2 , and impressive cycling stability for more than 2000â cycles at 5.0â mA cm-2 .
RESUMEN
Hydrogen peroxide (H2 O2 ) is a green oxidizer widely involved in a vast number of chemical reactions. Electrochemical reduction of oxygen to H2 O2 constitutes an environmentally friendly synthetic route. However, the oxygen reduction reaction (ORR) is kinetically sluggish and undesired water serves as the main product on most electrocatalysts. Therefore, electrocatalysts with high reactivity and selectivity are highly required for H2 O2 electrosynthesis. In this work, a synergistic strategy is proposed for the preparation of H2 O2 electrocatalysts with high ORR reactivity and high H2 O2 selectivity. A Co-Nx -C site and oxygen functional group comodified carbon-based electrocatalyst (named as Co-POC-O) is synthesized. The Co-POC-O electrocatalyst exhibits excellent catalytic performance for H2 O2 electrosynthesis in O2 -saturated 0.10 m KOH with a high selectivity over 80% as well as very high reactivity with an ORR potential at 1 mA cm-2 of 0.79 V versus the reversible hydrogen electrode (RHE). Further mechanism study identifies that the Co-Nx -C sites and oxygen functional groups contribute to the reactivity and selectivity for H2 O2 electrogeneration, respectively. This work affords not only an emerging strategy to design H2 O2 electrosynthesis catalysts with remarkable performance, but also the principles of rational combination of multiple active sites for green and sustainable synthesis of chemicals through electrochemical processes.
RESUMEN
As the key of hydrogen economy, electrocatalytic hydrogen evolution reactions (HERs) depend on the availability of cost-efficient electrocatalysts. Over the past years, there is a rapid rise in noble-metal-free electrocatalysts. Among them, transition metal carbides (TMCs) are highlighted due to their structural and electronic merits, e.g., high conductivity, metallic band states, tunable surface/bulk architectures, etc. Herein, representative efforts and progress made on TMCs are comprehensively reviewed, focusing on the noble-metal-like electronic configuration and the relevant structural/electronic modulation. Briefly, specific nanostructures and carbon-based hybrids are introduced to increase active-site abundance and to promote mass transportation, and heteroatom doping and heterointerface engineering are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted HER kinetics. Finally, a perspective on the future development of TMC electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials in energy chemistry.
RESUMEN
To advance hydrogen economy, noble-metal-free electrocatalysts with good efficiency are urgently demanded. They can be developed from metal-organic frameworks (MOFs) with abundant structure-variety, in which a controlled pyrolysis is desired to rationalize nanostructure and maximize catalytic activity. Herein, the efficient regulation is proposed for the first time on the carbon-shell of MOFs-derived Co@NC nanocomposites via varying temperature and flow-rate during pyrolysis, enabling the good accessibility and the electronic optimization of active Co cores. With moderated temperature and flow-rate, the resulting ultrathin carbon-shell, on the one hand, renders Co cores easily accessible to electrolytes and, on the other hand, promotes the electronic penetration to optimize metallic Co active sites. As expected, the optimal Co@NC affords the benchmarking performance of noble-metal-free electrocatalysts in hydrogen evolution and oxygen reduction reactions, featured by the low overpotentials, the striking kinetic metrics, and the outstanding long-term stability. Elucidating the feasibility to design efficient electrocatalysts via controlled MOFs pyrolysis, this work will open up new opportunities for the development of cost-effective materials in the energy field.
RESUMEN
Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have drawn much attention due to their unique physical and chemical properties. Using TMDs as templates for the generation of 2D sandwich-like materials with remarkable properties still remains a great challenge due to their poor solvent processability. Herein, MoS2 -coupled sandwich-like conjugated microporous polymers (M-CMPs) with high specific surface area were successfully developed by using functionalized MoS2 nanosheets as template. As-prepared M-CMPs were further used as precursors for preparation of MoS2 -embedded nitrogen-doped porous carbon nanosheets, which were revealed as novel electrocatalysts for oxygen reduction reaction with mainly four-electron transfer mechanism and ultralow half-wave potential in comparison with commercial Pt/C catalyst. Our strategy to core-shelled sandwich-like hybrids paves a way for a new class of 2D hybrids for energy conversion and storage.