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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]

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices. [ABSTRACT FROM AUTHOR]

Iron-based single-site catalysts hold immense potential for achieving highly selective chemical processes, with the added advantage of iron being an earth-abundant metal. They are widely explored in electrocatalysis for oxygen reduction and display promising catalytic activity for organic transformations. In particular, FeNx@C catalysts are active for the reduction of nitroarene into aromatic amines. Yet, they are difficult to mass-produce, and most preparation methods fail to avoid single site aggregation. Here we prepared FeNx@C catalysts from bio-derived compounds, xylose and haemoglobin, in a simple two-step process. Since haemoglobin naturally contains FeNx single-sites, we successfully repurposed them into hydrogenation catalytic centers and avoided their aggregation during the preparation of the material. Their single-site nature was demonstrated by aberration-corrected transmission electron microscopy and X-ray absorption techniques. They were shown to be active for transfer hydrogenation of nitroarenes into anilines, with excellent substrate selectivity and recyclability, as demonstrated by the preserved yield across seven catalytic cycles. We also showed that FeNx@C could be used to prepare 2-phenylbenzimidazole through a reduction/condensation tandem. Our work shows for the first time the viability of biomass precursors to prepare Fe single-site hydrogenation catalysts. [ABSTRACT FROM AUTHOR]

Alkaline oxygen reduction reaction (ORR) presents an important role for energy conversion technologies and requires the development of an efficient electrocatalyst. Pt-based catalysts provide suitable activity; however, Pt production accessibility and high costs create hurdles to their commercial implementation. Fe coordinated within N-doped carbon materials (Fe N C) are a promising alternative due to their high ORR catalytic activity, although the currently commercially available Fe N C materials rely on harsh synthetic protocols which can lead to increased environmental impacts. In this work we target this issue by taking advantage of an oily sludge waste currently generated in refineries to synthesize Fe N C materials, thus, avoiding the environmental impact caused by the management of this waste. The solid particles within oily sludge, which present a high concentration of C and Fe, were combined by different nitrogen sources and pyrolyzed at high temperatures. The prepared materials present a hierarchical pore structure with surface areas up to 547 m2 g−1. X-ray photoelectron spectroscopy analysis found that the impregnation of N using phenanthroline promotes the formation of pyridinic-N structures, which enhances the ORR performance compared to melamine doping. Additional doping of Fe with phenanthroline results in an ORR mass activity of 1.23 ± 0.04 A g FeNC −1 at 0.9 V RHE, iR-free in a rotating disc electrode (0.1 M KOH). This catalyst also shows a lower relative loss in activity at 0.9 V RHE after 8000 cycles in O 2 -saturated conditions compared to a commercial FeNC catalyst, PMF D14401, (−63.5 vs −69 %, respectively), demonstrating promise as a cheap and simple route to Fe N C catalysts for alkaline ORR. [Display omitted] [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]

The next generation of proton exchange membrane fuel cells (PEMFCs) require a substantial reduction or elimination of Pt-based electrocatalyst from the cathode, where O 2 reduction takes place. The most promising alternative to Pt is atomic Fe embedded in N-doped C (Fe–N–C). Successful incorporation of Fe–N–C in PEMFCs relies on a thorough understanding of the catalyst layer properties, both ex situ and in situ , with tailored electrode interface engineering. To help resolve this conundrum, we provide a quantitative protocol on the optimisation of I/C for Fe–N–Cs. It is demonstrated that a high pore volume (3.33 cm3 g−1 FeNC) Fe–N–C catalyst requires a sufficiently high ionomer to catalyst mass ratio (I/C, 2.8≤I/C ≤ 4.2) for optimum PEMFC activity under H 2 /O 2. Emerging electrochemical techniques (distribution of relaxation times and Fourier transformed alternating current voltammetry) were used to deconvolute for the first time the trade-off between proton and electron resistance and accessible FeN x active site density with increasing ionomer loading. These findings highlight the significant impact of tuning the I/C ratio based on the catalyst layer properties and feature the power of evolving electrochemical tools for optimising performance in PEMFCs and other electrochemical devices. [Display omitted] • In situ FTacV quantified Fe–N–C electrochemical active site density in fuel cell. • Fe–N–C active site density and current density correlated with ionomer loading. • DRT quantified resistance to proton transport and oxygen diffusion in fuel cell. • Fe–N–C to ionomer ratio optimised based on quantitative protocol. [ABSTRACT FROM AUTHOR]

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]

Dual‐Metal Atom Electrocatalysts In article number 2102715, Maria Magdalena Titirici, Ifan E. L. Stephens and co‐workers comprehensively review dual‐metal atom electrocatalysts, providing insight into how this class of materials could lead to a step change in catalytic performance over single‐atom and metallic electrocatalysts. They discuss key challenges and opportunities in the synthesis, characterization, and electrochemical testing of dual‐metal atom electrocatalysts. [ABSTRACT FROM AUTHOR]

Keywords: CO 2 reduction; electrocatalysts; N 2 reduction; O 2 evolution; O 2 reduction EN CO 2 reduction electrocatalysts N 2 reduction O 2 evolution O 2 reduction 1 1 1 01/25/22 20220120 NES 220120 B Dual-Metal Atom Electrocatalysts b In article number 2102715, Maria Magdalena Titirici, Ifan E. L. Stephens and co-workers comprehensively review dual-metal atom electrocatalysts, providing insight into how this class of materials could lead to a step change in catalytic performance over single-atom and metallic electrocatalysts. CO 2 reduction, electrocatalysts, N 2 reduction, O 2 evolution, O 2 reduction They discuss key challenges and opportunities in the synthesis, characterization, and electrochemical testing of dual-metal atom electrocatalysts. [Extracted from the article]

The electrochemical CO2 reduction reaction (CO2RR) to value‐added chemicals with renewable electricity is a promising method to decarbonize parts of the chemical industry. Recently, single metal atoms in nitrogen‐doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, two catalysts are synthesized through a decoupled two‐step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso‐porous structure results in the highest reported electrochemical active site utilization based on in situ nitrite stripping; up to 59±6% for NiNC. Ex situ X‐ray absorption spectroscopy (XAS) confirms the penta‐coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. The density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, it is found that the turnover frequencies (TOFs) of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates. [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]

Carbon-supported single metal atoms coordinated to nitrogen have recently emerged as efficient electrocatalysts for the electrochemical CO 2 reduction reaction (CO2RR) to CO; although the presence of aggregated metallic species can decrease Faradaic efficiency, catalyst utilization and promote the hydrogen evolution reaction. In this work, we employ our recent synthetic protocol for producing single and dual Fe atoms in a high surface area C 2 N-derived nitrogen-doped carbon and test the catalysts for CO 2 reduction. The higher resolution of the X-ray absorption spectroscopy that we employed herein, relative to our previous report, allowed us to more accurately pinpoint the dominant site as pentacoordinated Fe single atoms. The material displays high active site utilization of 25.1 ± 1.2% (based on in situ nitrite stripping experiments). Additionally, a Faradaic efficiency of 98% for the CO2RR to CO was obtained, with a turnover frequency of 2.5 e− site−1 s−1, at -0.56 V vs a reversible hydrogen electrode (RHE); on par with state-of-the-art Au catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]