Egg‐Derived Mesoporous Carbon Microspheres as Bifunctional Oxygen Evolution and Oxygen Reduction Electrocatalysts

Abstract

Furthermore, the electronic and catalytic property modulation are mostly achieved by extrinsic doping of heteroatoms. [20][21][22] However, the capability of solely utilizing the intrinsic composition of biomass for catalysts has not been demonstrated.On the other hand, mesoporous materials represent another large category of materials for catalysis [21][22][23] and energy applications, [ 15 ] due to their high surface areas, ordered mesostructures, and tunable pore sizes. A variety of mesoporous materials have been synthesized and loaded with different metal, [ 22 ] nonmetal, [ 23 ] or even biomaterial components [ 17 ] toward high catalytic activity. Nonetheless, the development of mesoporous materialbased bifunctional OER and ORR electrocatalysts, especially from ecofriendly biomass, has seldom been reported. [ 18 ] Eggs, as one of natural living organisms, contain abundant proteins, cholesterols, and lecithins that can be utilized as a unique precursor for carbon frameworks. More importantly, the resourceful metal and nonmetal elements (e.g., N, P, O, and Fe) in egg organisms may enable intrinsic, homogeneous doping of carbon framework to achieve catalytic activity, waiving the need to adding extrinsic doping sources. Herein, we report an ecofriendly and facile way to synthesize homogeneously N, P, and Fe codoped mesoporous carbon microspheres (egg-CMS) from eggs, using a high-throughput spray-drying technique without the extrinsic doping sources. Tetraethyl orthosilicate (TEOS) was fi rst mixed and spray dried with eggs, and subsequently etched to obtain mesostructures. Remarkably, the as-obtained codoped egg-CMS possesses a large specifi c surface area with high pore volume and shows excellent electrocatalytic performances, including low onset potentials, Tafel slopes, large current densities, and superior stabilities for both ORR and OER. Furthermore, rechargeable Zn-air batteries fabricated with this bifunctional egg-CMS electrocatalyst show an initial cell voltage of 1.28 V, which can be well maintained at ≈1 V after 30 charge-discharge cycles. Results and DiscussionThe main components in eggs include amino acids, cholesterols, and lipids, [ 24 ] whose structural formula is displayed A bifunctional evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts are developed, based on codoped mesoporous carbon microspheres from ecofriendly biomass of eggs without the introduction of extrinsic dopants, via a facile and high-throughput spray-drying process. The obtained egg-derived mesoporous carbon microspheres (egg-CMS) present large specifi c surface area and high pore volume, as well as abundant dopant types including nitrogen, phosphorous, and iron that are originated from the innate protein and small organic molecule contents. When fabricated as OER or ORR catalysts, these egg-CMS exhibit low onset potentials, high current densities, small Tafel slopes, and excellent stabilities. As a proof-of-concept, a rechargeable Zn-air battery is demonstrated using the high-active egg-CMS as a bifu...

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