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Atomically dispersed iron–nitrogen–carbon catalysts are promised, low‐cost, and high‐performance electrocatalysts for the Oxygen Reduction Reaction (ORR) in fuel cells. However, most Fe–N–C materials are produced via pyrolysis at a high temperature and it is difficult to characterise the precise Fe–N configurations. This can lead to confusion surrounding the best chemical and coordination environment for Fe and understanding the subsequent ORR mechanisms. In this work, Fe porphyrin is used to produce a specific Fe–N environment, therefore allowing the role and activity of this environment to be studied. Carbon nanotubes (CNTs) are covalently functionalized with iron 5,10,15,20‐triphenylporphyrin (FeTPP) motifs via aryl diazonium methodology, enabling the exact role of only the Fe‐Pyrrolic N4 configuration of FeTPP in ORR to be studied and better understood. Upon covalent functionalization, a high electrochemical active site density of 1.12 × 1015 sites cm−2, approximately six‐fold more than that of noncovalently functionalized samples with 12.7% electrochemical active site. The heightened active site density and superior electrochemical active site utilization (12.7%) lead to the more favorable 4‐electron pathway for the ORR. Furthermore, a preliminary discussion regarding the selectivity of the ORR pathway is initiated. [ABSTRACT FROM AUTHOR]

Iron–nitrogen–carbon (FeNC) electrocatalysts are emerging as a low-cost alternative to Pt-based materials for electrochemical oxygen reduction at the cathode of alkaline exchange membrane hydrogen fuel cells. The valorisation of waste biomass is a sustainable pathway that could allow the large-scale production of such catalysts. By means of hydrothermal carbonization (HTC), a biomass-derived carbohydrate can be converted into a carbonaceous framework, however, the electrocatalytic performance of the metal–nitrogen–carbon electrocatalysts prepared through HTC is suboptimal owing to the lack of microporosity in the highly crosslinked carbon frameworks. In this work, we address this issue by adding polystyrene sulfonate (kayexalate) in the HTC of xylose. Kayexalate's negative charges mitigate particle aggregation, resulting in smaller carbon-based particles, with the O2 activation leading to a four-fold increase in specific surface area (127 vs. 478 m2 g−1). Subsequent high-temperature pyrolysis in the presence of an N and Fe source leads to an active FeNC. This produces a corresponding increase in the electrocatalytic activity for the oxygen reduction in alkaline media in a rotating disk electrode (1.45 vs. 14.3 A g−1 at 0.8 V vs. RHE) and in a gas diffusion electrode at high current densities (≥2 A cm−2). The sustainable character of the reported catalyst as well as the high electrocatalytic activity at industrially relevant current densities provides a pathway to catalyst design for low-cost cathodes in alkaline exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Sluggish kinetics in the oxygen reduction reaction (ORR) require significant quantities of expensive Pt-based nanoparticles on carbon (Pt/C) at the cathode of proton exchange membrane fuel cells (PEMFCs). This catalyst requirement hinders their large-scale implementation. Single atom Fe in N-doped C (Fe–N–C) electrocatalysts offer the best non-Pt-based ORR activities to date, but their environmental impacts have not been studied and their production costs are rarely quantified. Herein, we report a comparative life-cycle assessment and techno-economic analysis of replacing Pt/C with Fe–N–C at the cathode of an 80 kW PEMFC stack. In the baseline scenario (20 gPt/Cvs. 690 gFe–N–C), we estimate that Fe–N–C could reduce damages on ecosystems and human health by 88–90% and 30–44%, respectively, while still increasing global warming potential by 53–92% and causing a comparable impact on resource depletion. The environmental impacts of Pt/C predominantly arise from the Pt precursor while those of Fe–N–C are presently dominated by the electricity consumption. The monetized costs of environmental externalities for both Fe–N–C and Pt/C catalysts exceed their respective direct production costs. Based on catalyst performance with learning curve analysis at 500 000 PEMFC stacks per annum, we estimate replacing Pt/C with Fe–N–C would increase PEMFC stack cost from 13.8 to 41.6 USD per kW. The cost increases despite a reduction in cathode catalyst production cost from 3.41 to 0.79 USD per kW (excluding environmental externalities). To be cost-competitive with a Pt-based PEMFC stack delivering 2020 US Department of Energy target of 1160 mW cm−2 (at 0.657 V), the same stack with an Fe–N–C cathode would need to reach 874 mW cm−2, equivalent to a 200% performance improvement. These findings demonstrate the need for continued Fe–N–C activity development with sustainable synthesis routes in mind to replace Pt-based cathode catalyst in PEMFCs. Based on forecasting scenarios of fuel cell vehicle deployment targets, we find that Pt consumption would be constrained by Pt supply. [ABSTRACT FROM AUTHOR]

Electrochemical clean energy conversion and the production of sustainable chemicals are critical in the journey to realizing a truly sustainable society. To progress electrochemical storage and conversion devices to commercialization, improving the electrocatalyst performance and cost are of utmost importance. Research into dual‐metal atom catalysts (DACs) is rising in prominence due to the advantages of these sites over single‐metal atom catalysts (SACs), such as breaking scaling relationships for the adsorption energy of reaction intermediates and synergistic effects. This review provides an examination of the fundamental theoretical principles and experimental electrochemical performance of DACs in idealized half cells, as well as fuel cells, before proceeding to analyze the methods used for producing and identifying DACs. Current challenges and potential future research directions of DACs are also discussed. [ABSTRACT FROM AUTHOR]

Atomically dispersed transition metal‐nitrogen‐carbon catalysts are emerging as low‐cost electrocatalysts for the oxygen reduction reaction in fuel cells. However, a cost‐effective and scalable synthesis strategy for these catalysts is still required, as well as a greater understanding of their mechanisms. Herein, iron, nitrogen co‐doped carbon spheres (Fe@NCS) have been prepared via hydrothermal carbonization and high‐temperature post carbonization. It is determined that FeN4 is the main form of iron existing in the obtained Fe@NCS. Two different precursors containing Fe2+ and Fe3+ are compared. Both chemical and structural differences have been observed in catalysts starting from Fe2+ and Fe3+ precursors. Fe2+@NCS‐A (starting with Fe2+ precursor) shows better catalytic activity for the oxygen reduction reaction. This catalyst is studied in an anion exchange membrane fuel cell. The high open‐circuit voltage demonstrates the potential approach for developing high‐performance, low‐cost fuel cell catalysts. [ABSTRACT FROM AUTHOR]