Tremendous developments in energy storage and conversion technologies urges researchers to develop inexpensive, greatly efficient, durable and metal-free electrocatalysts for tri-functional electrochemical reactions, namely oxygen reduction reactions (ORRs), oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs). In these regards, this present study focuses upon the synthesis of porous carbon (PC) or N-doped porous carbon (N-PC) acquired from golden shower pods biomass (GSB) via solvent-free synthesis. Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies confirmed the doping of nitrogen in N-PC. In addition, morphological analysis via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) provide evidence of the sheet-like porous structure of N-PC. ORR results from N-PC show the four-electron pathway (average n = 3.6) for ORRs with a Tafel slope of 86 mV dec−1 and a half-wave potential of 0.76 V. For OERs and HERs, N-PC@Ni shows better overpotential values of 314 and 179 mV at 10 mA cm−2, and its corresponding Tafel slopes are 132 and 98 mV dec−1, respectively. The chronopotentiometry curve of N-PC@Ni reveals better stability toward OER and HER at 50 mA cm−2 for 8 h. These consequences provide new pathways to fabricate efficient electrocatalysts of metal-free heteroatom-doped porous carbon from bio-waste/biomass for energy application in water splitting and metal air batteries.
It is highly desirable to develop an energy generation system comprising a low-cost and earth-abundant non-noble metal catalyst for bifunctional electrocatalysis with good overall process performance, especially for applications in fuel cells or metal-air batteries. In this report, we show that nickel cobalt phosphite (NiCoÀ Phi) decorated with carbon nanotubes (CNTs) can perform as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions (OER and ORR, respectively). The NiCoÀ Phi/CNT composite is synthesized by employing a simple, single-step hydrothermal method. The morphology of the composite consists of nanorod bundles of NiCoÀ Phi decorated with CNTs. The synthesized NiCoÀ Phi/CNT composite exhibits enhanced electrochemical OER activity with an overpotential of 400 mV at a current density of 10 mA/cm 2 and a Tafel slope value of 117 mV dec À 1 in 1 M KOH, possessing high stability towards the OER for 20 h. The ORR using the same catalyst shows an onset potential of 0.75 V and a Tafel slope of 100 mV dec À 1 in 0.1 M KOH with high-yield production of H 2 O 2 (85 %). The predominant formation of H 2 O 2 occurs mainly through a two-electron transfer process, as established by mass-controlled kinetic studies and has not been observed previously in these phosphorous oxy anion-based materials. The superior bifunctional nature of NiCoÀ Phi/CNT towards the OER and ORR arises from the synergistic effect of doped metal phosphites and CNTs.
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