overall energy conversion efficiency of these devices. Currently, noble Pt-based materials are regarded as state-of-the-art electrocatalysts for the sluggish ORR. [6][7][8][9] Unfortunately, the scarcity, high cost, and poor stability hamper their commercial application. Tremendous effort has accordingly been devoted to exploring highly efficient and low-cost alternatives to Pt-based electrocatalysts. Among the various candidates, earth-abundant transition metal (TM)-based species embedded within nitrogen-doped carbonaceous support to form hybrid composites (TM@N-C) have received increasing attention owing to their unique electronic structure and synergistic effect.To rationally design TM@N-C electrocatalysts for the ORR, modulating the electronic structure or optimizing the geometric structure have been adopted to boost the catalytic process. The former strategy mainly involves heteroatom doping or alloying TM species to reduce the kinetic energy barriers and thus improve intrinsic activity while the latter strategy concentrates on the construction of the desired morphology and pore structure of the electrocatalyst to increase the accessible surface areas, ensure rapid mass transport to all accessible active sites, and provide structural protection. For example, Fu et al. synthesized an electrocatalyst consisting of NiCo alloy nanoparticles anchored on porous fibrous carbon (PFC) aerogels via Engineering non-precious transition metal (TM)-based electrocatalysts to simultaneously achieve an optimal intrinsic activity, high density of active sites, and rapid mass transfer ability for the oxygen reduction reaction (ORR) remains a significant challenge. To address this challenge, a hybrid composite consisting of Fe x Co alloy nanoparticles uniformly implanted into hierarchically ordered macro-/meso-/microporous N-doped carbon polyhedra (HOMNCP) is rationally designed. The combined results of experimental and theoretical investigations indicate that the alloying of Co enables a favorable electronic structure for the formation of the *OH intermediate, while the periodically trimodal-porous structured carbon matrix structure not only provides highly accessible channels for active site utilization but also dramatically facilitates mass transfer in the catalytic process. As expected, the Fe 0.5 Co@HOMNCP composite catalyst exhibits extraordinary ORR activity with a half-wave potential of 0.903 V (vs reversible hydrogen electrode), surpassing most Co-based catalysts reported to date. More remarkably, the use of the Fe 0.5 Co@HOMNCP catalyst as the air electrode in a zinc-air battery results in superior open-circuit voltage and power density compared to a commercial Pt/C + IrO 2 catalyst. The results of this study are expected to inspire the development of advanced TMbased catalysts for energy storage and conversion applications.
Developing an efficient and non‐precious pH‐universal hydrogen evolution reaction electrocatalyst is highly desirable for hydrogen production by electrochemical water splitting but remains a significant challenge. Herein, a hierarchical structure composed of heterostructured Ni2P‐Ni12P5 nanorod arrays rooted on Ni3S2 film (Ni2P‐Ni12P5@Ni3S2) via a simultaneous corrosion and sulfidation is built followed by a phosphidation treatment toward the metallic nickel foam. The combination of theoretical calculations with in/ex situ characterizations unveils that such a unique sequential phase conversion strategy ensures the strong interfacial coupling between Ni2P and Ni12P5 as well as the robust stabilization of 1D heteronanorod arrays by Ni3S2 film, resulting in the promoted water adsorption/dissociation energy, the optimized hydrogen adsorption energy, and the enhanced electron/proton transfer ability accompanied with an excellent stability. Consequently, Ni2P‐Ni12P5@Ni3S2/NF requires only 32, 46, and 34 mV overpotentials to drive 10 mA cm−2 in 1.0 m KOH, 0.5 m H2SO4, and 1.0 m phosphate‐buffered saline electrolytes, respectively, exceeding almost all the previously reported non‐noble metal‐based electrocatalysts. This work may pave a new avenue for the rational design of non‐precious electrocatalysts toward pH‐universal hydrogen evolution catalysis.
The electrochemical performance of lithium‐sulfur (Li‐S) batteries is severely hindered by the sluggish sulfur redox kinetics and the shuttle effect of lithium polysulfides (LiPSs). Herein, an integrated composite catalyst consisting of Co nanoparticles and single‐atom (SA) Zn co‐implanted in nitrogen‐doped porous carbon nanosheets grafted with carbon nanotubes (Co/SA‐Zn@N‐C/CNTs) is rationally developed toward this challenge. Experimental and theoretical investigations indicate that the synergistically dual active sites of Co and atomic Zn‐N4 moieties with an optimal charge redistribution not only strongly confine the LiPSs but also effectively catalyze its conversion reactions by lowering the energy barrier from Li2S2 to Li2S while the N‐doped porous carbon‐grafted CNTs enables a large surface area for more active site exposure and provides a fast electron/ion pathway. Benefiting from synergies, Li‐S batteries equipped with the Co/SA‐Zn@N‐C/CNTs‐based sulfur cathode exhibit a high reversible capacity of 1302 mAh g−1 at 0.2 C and a low capacity fading rate of 0.033% per cycle over 800 cycles at 1 C. Moreover, a high areal capacity of 4.5 mAh cm−2 at 0.2 C with the sulfur loading of 5.1 mg cm−2 can be achieved. The present work may provide new insight into the design of high‐performance sulfur‐based cathodes for Li‐S batteries.
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