Iron, nitrogen-codoped carbon (Fe-N-C) nanocomposites have emerged as viable electrocatalysts towards oxygen reduction reaction (ORR) due to the formation of FeN x C y moieties. In this study, results from first-principles calculations show a nearly linear correlation of the energy barriers of key reaction steps with the Fe magnetic moment. Experimentally, when single Cu sites are incorporated into Fe-N-C aerogels (denoted as NCAG/Fe-Cu), the Fe centers exhibit a reduced magnetic moment and markedly enhanced ORR activity within a wide pH range of 0~14 . With the NCAG/Fe-Cu nanocomposites used as the cathode catalyst in a neutral/quasi-solid aluminum-air and alkaline/quasi-solid zinc-air battery, both achieve a remarkable performance with an ultrahigh open-circuit voltage of 2.00 and 1.51 V, large power density of 130 and 186 mA cm -2 , and good mechanical flexibility, all markedly better than those with commercial Pt/C or Pt/C-RuO 2 catalysts at the cathode.

Theory-Guided Regulation of FeN4 Spin State by Neighboring Cu Atoms for Enhanced Oxygen Reduction Electrocatalysis in Flexible Metal-Air Batteries.

Searching for cheap, efficient, and stable oxygen electrocatalysts is vital to promote the practical performance of Zn-air batteries with high theoretic energy density. Herein, a series of Co nanoparticles and highly dispersed Fe loaded on N-doped porous carbon substrates are prepared through a “double-solvent” method with in situ doped metal-organic frameworks as precursors. The optimized catalysts exhibit excellent performance for oxygen reduction and evolution reaction. Furthermore, rechargeable Zn-air batteries with designed catalysts demonstrate higher peak power density and better cycling stability than those with commercial Pt/C+RuO2. According to structure characterizations and electrochemical tests, the interaction of Co nanoparticles and highly dispersed Fe contributes to the superior performance for oxygen electrocatalysis. In addition, large specific surface areas, porous structures and interconnected three-dimensional carbon networks also play important roles in improving oxygen electrocatalysis. This work provides inspiration for rational design of advanced oxygen electrocatalysts and paves a way for the practical application of rechargeable Zn-air batteries. 

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MOF-Derived Co and Fe Species Loaded on N-Doped Carbon Networks as Efficient Oxygen Electrocatalysts for Zn-Air Batteries

Fabrication of hybrid trimetallic-organic framework-derived N, C co-doped Ni–Fe–Mn–P ultrathin nanosheet electrocatalyst demonstrating excellent performance with low overpotentials and cell voltage for HER, OER and overall water splitting.

A hybrid trimetallic–organic framework-derived N, C co-doped Ni–Fe–Mn–P ultrathin nanosheet electrocatalyst for proficient overall water-splitting

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development of new energy technologies. This review summarizes the recent research progress of non-precious transition metal single-atom catalysts (NPT-SACs) for the oxygen reduction reaction (ORR) in Zn-air batteries and fuel cells. Some commonly used preparation methods and their advantages/disadvantages have been summarized. The factors affecting the ORR performances of NPT-SACs have been focused upon, such as the substrate type, coordination environment and nanocluster effects. The loading mass of a metal atom has a direct effect on the ORR performances. Some general strategies for stabilizing metal atoms are included. This review points out some existing challenges of NPT-SACs, and also provides ideas for designing and synthesizing NPT-SACs with excellent ORR performances. The large-scale preparation and commercialization of NPT-SACs with excellent ORR properties are prospected.

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects.

It is a natural choice to realize the vision of wood‐inspired functional materials for energy engineering. Apart from being naturally abundant, renewable, and biodegradable, wood‐based devices possess hierarchically porous structures, mechanical integrity and flexibility, and tunable functionalities, holding the potential to significantly push the boundaries of efficient energy storage and conversion. Meanwhile, the hunting of batteries with superior energy/power output to redeem the ever‐growing energy demand has ignited a thick electrode conception, which is deemed as a burgeoning technic to maneuver the maximum active material loading at the device‐scale. As an integrated carbonaceous scaffold with hierarchical architecture and aligned channels, wood thick electrode ameliorates the ion/electron conductivities to strengthen the charge transfer kinetics. In this review, the rational design and unique prospects in the construction of wood thick electrodes that concerns over structural optimization and low‐tortuosity for integrated cell configuration are summarized. To trap the structure‐feature‐performance interplays, advanced wood thick electrode that opens an avenue in emerging energy chemistries such as supercapacitors, lithium‐ion/metal and post‐rechargeable batteries are also spotlighted with a standpoint on task‐tailored modification. Ultimately, the blueprint over ongoing challenges and upcoming opportunities for wood‐structured thick electrode is drawn to broaden their brand‐new energy talents.

Rational Design of Wood‐Structured Thick Electrode for Electrochemical Energy Storage

Developing a highly efficient, easy-to-fabricate and non-noble metal electrocatalyst is vital for the oxygen reduction reaction (ORR). Herein, we fabricate a single Fe site catalyst Fe1/d-CN by developing a double-layer MOF strategy. The Fe1/d-CN catalyst shows an excellent ORR activity in the pH-universal range, especially in alkaline electrolytes with a record-level half-wave potential of 0.950 V, exceeding those of almost all the reported non-noble electrocatalysts and the commercial Pt/C catalyst (0.863 V). Besides its exceptional ORR activity in alkaline electrolytes, it also exhibits comparable ORR activity to the commercial Pt/C catalyst in acidic and neutral electrolytes. We speculate that the sources of the excellent pH-universal ORR performance can be attributed to the regulation of the electronic structure of Fe centres and the excellent electron/proton transport capability that comes from the rich defects and hierarchical porous features of the Fe1/d-CN catalyst. More excitingly, the catalyst possesses remarkable durability, and exhibits a negligible decrease after 30k accelerated durability test (ADT) cycles in pH-universal media. The flexible quasi-solid-state alkaline rechargeable Zn–air batteries with the Fe1/d-CN catalyst as the cathode show superior performance such as a high OCV of 1.50 V and peak power density of 78.0 mW cm−2. Furthermore, the flexible quasi-solid-state neutral rechargeable Zn–air batteries also exhibited remarkable performance.

A pH-universal ORR catalyst with single-atom iron sites derived from a double-layer MOF for superior flexible quasi-solid-state rechargeable Zn–air batteries

Hanqin Sun

Papers

A pH-universal ORR catalyst with single-atom iron sites derived from a double-layer MOF for superior flexible quasi-solid-state rechargeable Zn–air batteries

Construction of ultra-stable NiFe armored catalyst for liquid and flexible quasi-solid-state rechargeable Zn-air batteries