ABSTRACT
Recent advancements on the development of nonprecious electrocatalysts with iron (Fe) incorporated active centers have generated confidence on realizing cost-effective proton exchange membrane fuel cells (PEMFCs). However, most of these catalysts that emerged as a substitution for the platinum supported on carbon (Pt/C) catalysts in oxygen reduction reaction (ORR) are active under basic conditions, and their feasibility in PEMFCs remains as a challenge. In this scenario, this work reports the synthesis of a Pt-free oxygen reduction electrocatalyst prepared by the annealing of polydopamine grown melamine foam. The prepared catalyst has a three-dimensional (3D) interconnected bilayer network structure possessing the carbon nitride backbone wrapped by graphitic carbon layer bearing iron carbides and nitrides as the active centers (3D-FePDC). Interestingly, the 3D-FePDC catalyst displayed an ORR activity both under acidic and basic conditions. Whereas the ORR performance of 3D-FePDC closely matches that of the commercial Pt/C in the basic medium, it displays only a low overpotential value of 60 mV under acidic conditions compared to its Pt counterpart. The kinetics of ORR on 3D-FePDC is found to be similar to the four-electron (4e) reduction pathway displayed by Pt/C. Testing of a PEMFC in a single cell mode by using 3D-FePDC as the cathode catalyst and Nafion membrane delivered a maximum power density of 278 mW cm-2, which is a promising value expected from a system based on the nonprecious metal cathode. Ultimately, as a cost-effective catalyst that can effectively perform irrespective of the pH conditions, 3D-FePDC offers significant prospects in the areas like fuel cells and metal-air batteries which work in acidic and/or basic conditions.
ABSTRACT
Ni- and Co-based materials have of late gained prominence over conventional noble metal-based ones as catalysts for energy devices. Here, a high performance catalyst which can facilitate both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was developed by anchoring a NiCo2O4 nanowire array on a carbon nanotube sponge (NCS). The three-dimensional morphology of NCS ensured efficient transport of the reactants and products on the catalyst surface, thereby improving the activity of the material. The prepared catalyst showed remarkable OER activity, requiring an overpotential of 280 mV, which is comparable to that of noble-metal catalysts. In addition to the noteworthy OER performance, the catalyst performed well with respect to the ORR. The total oxygen electrode activity overpotential of the catalyst was found to be 0.83 V, which is lower than that of commercial electrodes such as Pt/C and RuO2. A rechargeable Zn-air battery constructed with NCS had an open circuit voltage of 1.42 V, a maximum power density of 160 mW cm-2, and an energy density of 706 W h kg-1. NCS exhibited bifunctional electrocatalytic activity and high stability for both the OER and ORR, proving to be a good replacement for noble metal electrodes in rechargeable metal-air batteries.
ABSTRACT
We introduce a new and naturally abundant mild reducing agent, tannic acid, to improve the seed-mediated growth method for the synthesis of elongated tetrahexahedral Au nanocrystals enclosed with high-index (730) planes, at room-temperature. The control of the dimensions, plasmonics and electro-catalysis of such high-index faceted nanocrystals is remarkable.
ABSTRACT
Layer-separated 3D nitrogen doped graphene (NG) with an accessible interstitial surface and modulated activity characteristics for oxygen reduction in acidic medium could be prepared by wrapping NG sheets on in situ generated carbon nitride (CNx) tetrapods.
