Cobalt Nanoparticles Encapsulated with N-Doped Bamboo-Like Carbon Nanofibers as Bifunctional Catalysts for Oxygen Reduction/Evolution Reactions in a Wide pH Range

Abstract

Nonprecious bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts in wide pH electrolytes are crucial for the versatile use of electrochemical energy storage and conversion devices. Non-noble metal/nitrogendoped carbon (M−N/C) has been reported as a promising candidate for efficient and cost-effective bifunctional catalysts. Nevertheless, the stability and catalytic activity of M−N/C bifunctional catalysts in a wide pH range are still limited, especially in neutral and acidic electrolytes. Here, we synthesized directly grown N-doped bamboo-like carbon nanofiber-encapsulated cobalt nanoparticles on carbon flakes (Co−N/C fiber) via pyrolysis of 2D cobalt−zeolitic imidazolate framework and tubular g-C 3 N 4 . The in situ growth of N-doped carbon nanofiber incorporated with Co nanoparticles exposes large active sites and enhances charge transfer. Moreover, abundant mesopores with high loading of pyridinic-N, graphitic-N, Co@N/C, and Co−N x facilitate high catalytic activity in a wide pH condition. Co−N/C fiber shows superior ORR performance in alkaline, neutral, and acidic electrolytes with high onset potentials of 1.003, 0.820, and 0.800 V vs RHE, respectively. A comparable OER performance of Co−N/C fiber to the Ir/C benchmark in alkaline and neutral conditions can be obtained with 397 and 570 mV overpotentials at 10 mA cm −2 . Utilizing Co−N/ C fiber in alkaline and neutral Zn−air batteries exhibits power densities of 155 and 67 mW cm −2 , with excellent stability for over 180 h. This study offers a strategy for developing a bifunctional M−N/C catalyst that is applicable across a wide pH range via hybrid nanostructuring.

l-Alanine-Assisted Synthesis of a Hierarchically Porous Co@N–C/N-Ketjenblack Carbon Catalyst for Oxygen Reduction in Zn–Air Batteries

“…The high open-circuit voltage and power density of the Co@N–C/N–KB-built cell surpassed most recently reported cobalt-based catalysts (Table S1). ,,,,,− These results illustrated that Co@N–C/N–KB offered excellent performance in primary ZABs. Figure d shows that the Co@N–C/N–KB-built ZAB delivered a much higher specific capacity (790 mA h gZn –1 ) at a discharge current density of 5 mA cm –2 compared to the Pt/C-built cell (474 mA h gZn –1 ).…”

“…The ORR performance of Co@N–C/N–KB is among the best of recently reported cobalt-based catalysts (Table S1). ,,,,,− Koutecky–Levich (K–L) plots for ORR on Co@N–C/N–KB, extracted from LSV curves collected at rotation speeds ranging from 400 to 2500 rpm, are shown in Figure d. Apparently, the kinetic current density displayed a proportional increment upon elevating the rotation rate with accompaniment of a distinct diffusion-limited current density platform.…”

Advances and Perspective of Noble-Metal-Free Nitrogen-Doped Carbon for pH-Universal Oxygen Reduction Reaction Catalysts

“…During pyrolysis, evaporation of metallic Zn in the ZIF-8 creates a carbon material with a porous structure and nitrogen doping, possessing abundant micro/mesoporous structures with good surface area values as large as 458.31 m 2 g –1 . Meanwhile, reducing Co nodes and decomposition of imidazole ligands results in high loading of the active sites, including N-moieties, Co-N x /C, and Co@N/C. − The electrocatalyst showed E onset of 1.01 V tested in an alkaline electrolyte and 0.89 V when it was measured in both neutral and acidic electrolytes.…”

Nanostructured Ball-Milled Ni–Co–Mn Oxides from Spent Li-Ion Batteries as Electrocatalysts for Oxygen Evolution Reaction

“…The push for a higher portion of renewable energy production and usage increases the global demand for green energy conversion and storage devices, − such as water electrolyzers and metal–air batteries, which employ oxygen evolution reaction (OER) during their operation. To this end, the performance of such devices is still impeded by the sluggish OER, which necessitates a high overpotential for the four-electron path reaction. , To boost the OER kinetics, it is customary to utilize Ir- and Ru-based electrocatalysts due to their high catalytic activity. , However, their scarcity and high cost limit their utilization in wide applications. In response, transition metal ( e.g ., Ni, Co, Mn, Fe) oxide catalysts have emerged as promising alternatives due to their abundance and low cost. − …”

“…4,5 To boost the OER kinetics, it is customary to utilize Ir-and Ru-based electrocatalysts due to their high catalytic activity. 6,7 However, their scarcity and high cost limit their utilization in wide applications. In response, transition metal (e.g., Ni, Co, Mn, Fe) oxide catalysts have emerged as promising alternatives due to their abundance and low cost.…”