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The search for better and cheaper electrocatalysts is vital in the global transition to renewable energy resources. High-entropy alloys (HEAs) provide a near-infinite number of different alloys with approximately continuous properties such as catalytic activity. In this work, the catalytic activity for the electrochemical oxygen reduction reaction as a function of molar composition of Ag-Ir-Pd-Pt-Ru HEA is treated as a landscape wherein it is shown that the maxima are connected through ridges. By following the ridges, it is possible to navigate between the maxima using a modified nudged elastic band (NEB) model integrated in a machine learning NEB algorithm. These results provide a new understanding of the composition space being similar to an evolutionary landscape. This provides a possible new search and design strategy for new catalysts in which the composition of known catalysts can be optimized by following ridges rather than exploring the whole alloy composition space.

The electrochemical oxygen reduction reaction (ORR) is the key energy conversion reaction involved in fuel cells, metal-air batteries, and hydrogen peroxide production. Proliferation and improvement of the ORR requires wider use of new and existing high performance catalysts; unfortunately, most of these are still based on precious metals and become uneconomical in mass-use applications. Recent progress suggests that low cost and durable carbon materials can potentially be developed as efficient ORR catalysts. Significant efforts have been made in discovering fundamental catalytic mechanisms and engineering techniques to guide and enable viable regulation of both the ORR activity and selectivity of these carbon catalysts. Starting from the fundamental understanding, this report reviews recent progress in engineering carbon materials from exotic chemical doping to intrinsic geometric defects for improved ORR. On the basis of both theoretical and experimental investigations reported so far in this area, future improvements in carbon catalysts are also discussed, providing useful pathways for more efficient and reliable energy conversion technologies.

In the face of high cost and insufficient energy density of current lithium ion batteries, aqueous rechargeable Zn-air batteries with the advantages of low cost, environmental benignity, safety and high energy density are spotlighted in recent years. The practical application of Zn-air batteries, however, is severely restricted by the high overpotential, which is associated with the inherent sluggish kinetics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) of air electrocatalysts. Recently, engineering heterostructured/hybrid electrocatalysts by modulating the interface chemistry has been demonstrated as an effective strategy to improve the catalytic performance. Basically, there occur significant electronic effect, geometric effect, coordination effect, synergistic effect, and confinement effect at the heterostructure interface, which intensely affect electrocatalysts’ performance in terms of intrinsic activity, active site density and durability. In this review, the recent progress on development of heterostructured air electrocatalysts by interface engineering is summarized. Particularly, the potential relationship between interface chemistry and oxygen electrocatalysis kinetics is bridged and outlined. This review would provide a comprehensive and in-depth understanding of the crucial role of the well-defined interfaces towards fast oxygen electrocatalysis, and would offer a solid scientific basis for the rational design of efficient heterostructured air electrocatalysts and beyond.

The oxygen reduction reaction (ORR) limits the efficiency of oxygen-associated energy conversion in fuel cells and air-metal batteries. Today, expensive noble metal catalysts are often utilized to enhance the ORR and the resulting conversion efficiency in those devices. Hence, there is an intensive research to find efficient electrodes, exhibiting a favorable electronic structure, for ORR based on abundant materials that can be manufactured using low cost processes. In that context, metal-free carbon-based nanostructures and conducting polymers have been actively investigated. The negatively doped poly(benzimidazobenzophenanthroline) (BBL) as an efficient and stable oxygen cathode material is reported here. Compared to the benchmark p-doped conducting polymer poly(3,4-ethylendioxythiophene) (PEDOT), the BBL provides electrocatalysis that fully reduces dioxygen into water, via a (2 + 2)-electron transfer pathway with hydrogen peroxide (H2O2) as an intermediate; while PEDOT limits the ORR to H2O2. It is demonstrated that n-doped BBL is a promising air electrode material for low-cost and ecofriendly model fuel cells, without the need of any co-catalysts, and its performance is found to be superior to p-doped PEDOT air electrodes. Funding Agencies|Swedish Research CouncilSwedish Research Council [VR 2019-05577, 2016-03979]; AForsk [18-313]; Advanced Functional Materials Center at Linkoping University [2009-00971]; Karl Erik onnesjo Foundation

8 Figures.-- Supporting information.-- This is the peer reviewed version of the following article:Advanced Energy Materials: 202000075 (2020), which has been published in final form at https://doi.org/10.1002/aenm.202000075. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions., The oxygen reduction reaction (ORR) is one of the most important reactions in renewable energy conversion and storage devices. The full deployment of these devices depends on the development of highly active, stable, and low‐cost catalysts. Herein, a new hybrid material consisting of Na2Ta8O21−x/Ta2O5/Ta3N5 nanocrystals grown on N‐doped reduced graphene oxide is reported. This catalyst shows a significantly enhanced ORR activity by ≈4 orders of magnitude in acidic media and by ≈2 orders of magnitude in alkaline media compared to individual Na2Ta8O21−x on graphene. Moreover, it has excellent stability in both acid and alkaline media. It also has much better methanol tolerance than the commercial Pt/C, which is relevant to methanol fuel cells. The high ORR activity arises not only from the synergistic effect among the three Ta phases, but also from the concomitant nitrogen doping of the reduced graphene oxide nanosheets. A correlation between ORR activity and nitrogen content is demonstrated. Deep insights into the mechanism of the synergistic effect among these three Ta‐based phases, which boosts the ORR's kinetics, are acquired by combining specific experiments and density functional theory calculations., The authors wish to acknowledge the Ministère des Relations Internationales et de la Francophonie (Québec, Canada) and the Ministero degli Affari Esteri (Italy) for funding through “Mobility project Italy – Québec (Canada) no. QU13MO7”. S.S. and A.C.T. gratefully acknowledge the Fonds de Recherche du Québec-Nature et Technologies (FRQNT—team grant, Quebec, Canada), the Natural Sciences and Engineering Research Council of Canada (NSERC, Discovery Grants), and the Centre Québécois sur les Matériaux Fonctionnels (CQMF, Québec, Canada)

The electrochemical reduction of O2 via a two-electron reaction pathway to H2O2 provides a possibility for replacing the current anthraquinone process, enabling sustainable and decentralized H2O2 production. Here, a nitrogen-rich few-layered graphene (N-FLG) with a tunable nitrogen configuration is developed for electrochemical H2O2 generation. A positive correlation between the content of pyrrolic-N and the H2O2 selectivity is experimentally observed. The critical role of pyrrolic-N is elucidated by the variable intermediate adsorption profiles as well as the dependent negative shifts of the pyrrolic-N peak on X-ray adsorption near edge structure spectra. By virtue of the optimized N doping configuration and the unique porous structure, the as-fabricated N-FLG electrocatalyst exhibits high selectivity toward electrochemical H2O2 synthesis as well as superior long-term stability. To achieve high-value products on both the anode and cathode with optimized energy efficiency, a practical device coupling electrochemical H2O2 generation and furfural oxidation is assembled, simultaneously enabling a high yield rate of H2O2 at the cathode (9.66 mol h−1 gcat −1) and 2-furoic acid at the anode (2.076 mol m−2 h−1) under a small cell voltage of 1.8 V. Refereed/Peer-reviewed

The oxygen reduction reaction (ORR) is of great importance in energy-converting processes such as fuel cells and in metal-air batteries and is vital to facilitate the transition toward a nonfossil ...

Synthesis of highly efficient nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) superior to platinum (Pt) is still a big challenge. Herein, a new highly active ORR electrocatalyst is reported based on graphene layers-wrapped Fe/Fe5C2 nanoparticles supported on N-doped graphene nanosheets (GL-Fe/Fe5C2/NG) through simply annealing a mixture of bulk graphitic carbon nitride (g-C3N4) and ferrocene. An interesting exfoliation–denitrogen mechanism underlying the conversion of bulk g-C3N4 into N-doped graphene nanosheets is revealed. Owing to the high graphitic degree, optimum N-doping level and sufficient active sites from the graphene layers-wrapped Fe/Fe5C2 nanoparticles, the as-prepared GL-Fe/Fe5C2/NG electrocatalyst obtained at 800 °C exhibits outstanding ORR activity with a 20 mV more positive half-wave potential than the commercial Pt/C catalyst in 0.1 m KOH solution and a comparable onset potential of 0.98 V. This makes GL-Fe/Fe5C2/NG an outstanding electrocatalyst for ORR in alkaline solution.