Explore the vast range of titles available.

In this paper, an extensive characterisation of a range of carbon blacks (CB) with similar surface area but different surface chemistry is carried out by flow calorimetry, Raman spectroscopy, dynamic water vapour sorption, instrumental gas analysis, nitrogen adsorption/desorption and high potential chronoamperometry. Using these carbon materials as supports, Pt/CB electrocatalysts are prepared by microwave‐assisted polyol‐mediated synthesis in gram scale. Structural, morphological and electrochemical properties of the prepared electrocatalysts are evaluated by X‐ray diffraction, transmission electron microscopy, rotating disc electrode and in situ fuel cell characterisation of the corresponding membrane–electrode assemblies. The obtained results allow to establish a relationship between surface chemistry and electrochemical properties useful for the design of Pt/C catalyst layers with high performance and stability. Surface properties of carbon supports play a role in the electrochemical and durability characteristics of the corresponding electrocatalysts and catalyst layers: cathodes based on carbon blacks with hydrophobic character demonstrated improved oxygen reduction reaction activity, durability and mass transfer.

The cathodic oxygen reduction reaction (ORR) remains a major kinetic barrier to high-efficiency proton exchange membrane fuel cells (PEMFCs), motivating the search for electrocatalysts that combine high activity, low metal usage, and long-term durability. This review examines single-atom catalysts (SACs) as an emerging platform for fuel-cell cathodes with particular emphasis on how atomic-level design, ORR mechanism, and practical deployment barriers are interrelated. The review discusses the key ORR pathways, intermediate binding principles, and scaling constraints that govern cathodic performance, and examines how metal-center selection, coordination-environment engineering, support regulation, synergistic multi-site construction, and morphology-controlled synthesis can be used to tune intrinsic activity and stabilize isolated active sites. It further highlights mechanistic insights from theoretical and operando studies, with emphasis on structure–activity relationships, dynamic active-site evolution, and approaches to mitigate scaling limitations. Major barriers to practical deployment, including carbon corrosion, demetalization, agglomeration, peroxide/reactive oxygen species attack, and the persistent gap between half-cell metrics and membrane electrode assembly performance, are also critically assessed. Rather than treating these topics separately, this review discusses them as connected factors that together determine the viability of SAC-based fuel-cell cathodes.

One challenge for the commercial development of solid oxide fuel cells as efficient energy-conversion devices is thermo-mechanical instability. Large internal-strain gradients caused by the mismatch in thermal expansion behaviour between different fuel cell components are the main cause of this instability, which can lead to cell degradation, delamination or fracture 1 – 4 . Here we demonstrate an approach to realizing full thermo-mechanical compatibility between the cathode and other cell components by introducing a thermal-expansion offset. We use reactive sintering to combine a cobalt-based perovskite with high electrochemical activity and large thermal-expansion coefficient with a negative-thermal-expansion material, thus forming a composite electrode with a thermal-expansion behaviour that is well matched to that of the electrolyte. A new interphase is formed because of the limited reaction between the two materials in the composite during the calcination process, which also creates A-site deficiencies in the perovskite. As a result, the composite shows both high activity and excellent stability. The introduction of reactive negative-thermal-expansion components may provide a general strategy for the development of fully compatible and highly active electrodes for solid oxide fuel cells. Highly active but durable perovskite-based solid oxide fuel cell cathodes are realized using a thermal-expansion offset, achieving full thermo-mechanical compatibility between the cathode and other cell components.

Advanced electrocatalysts with low platinum content, high activity and durability for the oxygen reduction reaction can benefit the widespread commercial use of fuel cell technology. Here, we report a platinum-trimer decorated cobalt-palladium core-shell nanocatalyst with a low platinum loading of only 2.4 wt% for the use in alkaline fuel cell cathodes. This ternary catalyst shows a mass activity that is enhanced by a factor of 30.6 relative to a commercial platinum catalyst, which is attributed to the unique charge localization induced by platinum-trimer decoration. The high stability of the decorated trimers endows the catalyst with an outstanding durability, maintaining decent electrocatalytic activity with no degradation for more than 322,000 potential cycles in alkaline electrolyte. These findings are expected to be useful for surface engineering and design of advanced fuel cell catalysts with atomic-scale platinum decoration. Fuel cells are promising for converting fuel into electricity, but rely on development of high-performance catalysts for oxygen reduction. Here the authors report a highly durable platinum-trimer decorated cobalt-palladium catalyst with low platinum loading for electrocatalysis of oxygen reduction.

This contribution reports the discovery and analysis of a p -block Sn-based catalyst for the electroreduction of molecular oxygen in acidic conditions at fuel cell cathodes; the catalyst is free of platinum-group metals and contains single-metal-atom actives sites coordinated by nitrogen. The prepared SnNC catalysts meet and exceed state-of-the-art FeNC catalysts in terms of intrinsic catalytic turn-over frequency and hydrogen–air fuel cell power density. The SnNC-NH 3 catalysts displayed a 40–50% higher current density than FeNC-NH 3 at cell voltages below 0.7 V. Additional benefits include a highly favourable selectivity for the four-electron reduction pathway and a Fenton-inactive character of Sn. A range of analytical techniques combined with density functional theory calculations indicate that stannic Sn( iv )N x single-metal sites with moderate oxygen chemisorption properties and low pyridinic N coordination numbers act as catalytically active moieties. The superior proton-exchange membrane fuel cell performance of SnNC cathode catalysts under realistic, hydrogen–air fuel cell conditions, particularly after NH 3 activation treatment, makes them a promising alternative to today’s state-of-the-art Fe-based catalysts. For oxygen reduction and hydrogen oxidation reactions, proton-exchange membrane fuel cells typically rely on precious-metal-based catalysts. A p -block single-metal-site tin/nitrogen-doped carbon is shown to exhibit promising electrocatalytic and fuel cell performance.

Fe–N–C catalysts are the most promising platinum group metal-free oxygen-reduction catalysts, but they suffer from a low density of active metal sites and the so-called activity–stability trade-off. Here we report an Fe–N–C catalyst prepared by adding an optimal amount of H 2 to the traditional inert atmosphere during the thermal activation. The presence of H 2 significantly increases the total density of FeN 4 sites, suppressing the unstable pyrrolic-N-coordinated S1 sites and favouring the stable pyridinic-N-coordinated S2 sites with shortened Fe–N bond lengths. We propose that the intrinsically stable S2 sites are probably arranged in well-graphitized carbon layers, and the S1 sites exist in less-graphitized carbon. H 2 could remove unstable S1 sites and retain stable S2 sites during the pyrolysis to break the challenging activity–stability trade-off. The Fe–N–C catalyst in membrane electrode assemblies maintains a current density of 67 mA cm −2 at 0.8 V (H 2 –air) after 30,000 voltage cycles (0.60 to 0.95 V under H 2 –air), achieving encouraging durability and performance simultaneously. Fe–N–C catalysts are a promising alternative to precious metals in fuel cell cathodes, but they suffer from durability issues. Now, a preparation method is reported that allows increasing the active site density while also improving durability.

The development of catalysts free of platinum-group metals and with both a high activity and durability for the oxygen reduction reaction in proton exchange membrane fuel cells is a grand challenge. Here we report an atomically dispersed Co and N co-doped carbon (Co–N–C) catalyst with a high catalytic oxygen reduction reaction activity comparable to that of a similarly synthesized Fe–N–C catalyst but with a four-time enhanced durability. The Co–N–C catalyst achieved a current density of 0.022 A cm −2 at 0.9 V iR-free (internal resistance-compensated voltage) and peak power density of 0.64 W cm −2 in 1.0 bar H 2 /O 2 fuel cells, higher than that of non-iron platinum-group-metal-free catalysts reported in the literature. Importantly, we identified two main degradation mechanisms for metal (M)–N–C catalysts: catalyst oxidation by radicals and active-site demetallation. The enhanced durability of Co–N–C relative to Fe–N–C is attributed to the lower activity of Co ions for Fenton reactions that produce radicals from the main oxygen reduction reaction by-product, H 2 O 2 , and the significantly enhanced resistance to demetallation of Co–N–C. Platinum-group-metal-free, non-iron catalysts are highly desirable for the oxygen reduction reaction at proton exchange membrane (PEM) fuel cell cathodes, as they avoid the detrimental Fenton reactions. Now, a cobalt and nitrogen co-doped carbon catalyst with atomically dispersed porphyrin-like CoN 4 C 12 sites is reported with an improved activity and durability in PEM fuel cell conditions.

Atom trapping of scarce precious metals onto a suitable support at high temperatures has emerged as an effective approach to build thermally stable single-atom catalysts. Here, following a similar mechanism based on atom trapping through support effects, we demonstrate a reverse atom-trapping strategy to controllably extract strontium atoms from a rigid lanthanum strontium cobalt ferrite ((La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 O 3− δ , LSCF) surface with ease. The lattice oxygen redox activity of LSCF is accordingly fine-tuned, leading to enhanced cathode performance in a solid-oxide fuel cell. An over 30−70% increases in maximum power density of the single cells at intermediate temperatures is achieved by LSCF with surface strontium vacancies compared to the pristine surface. In addition, the strontium-deficient surface excludes strontium segregation and formation of electrochemically inert SrO islands, thus improving the longevity of the cathode. This development can be broadly applicable for modifying structurally stable oxide surfaces, and opens more possibilities of scalable single-atom extraction strategies. Atom trapping is a well-established route to prepare single-atom catalysts. Here the authors propose a reverse atom-trapping strategy in which surface strontium atoms of LSCF fuel cell cathodes are extracted by MoO 3 , forming single strontium vacancies on LSCF in a controllable manner and tuning its performance for the oxygen reduction reaction.

The limited durability of metal-nitrogen-carbon electrocatalysts severely restricts their applicability for the oxygen reduction reaction in proton exchange membrane fuel cells. In this study, we employ the chemical vapor modification method to alter the configuration of active sites from FeN 4 to the stable monosymmetric FeN 2 +N’ 2 , along with enhancing the degree of graphitization in the carbon substrate. This improvement effectively addresses the challenges associated with Fe active center leaching caused by N-group protonation and free radicals attack due to the 2-electron oxygen reduction reaction. The electrocatalyst with neoteric active site exhibited excellent durability. During accelerated aging test, the electrocatalyst exhibited negligible decline in its half-wave potential even after undergoing 200,000 potential cycles. Furthermore, when subjected to operational conditions representative of fuel cell systems, the electrocatalyst displayed remarkable durability, sustaining stable performance for a duration exceeding 248 h. The significant improvement in durability provides highly valuable insights for the practical application of metal-nitrogen-carbon electrocatalysts. The limited durability of metal-nitrogen-carbon electrocatalysts hinders their use in proton exchange membrane fuel cells for the oxygen reduction reaction. Here the authors transform active sites from FeN4 to stable monosymmetric FeN2 + N’2 via chemical vapor modification, resulting in enhanced improving the durability of the catalyst.

To achieve the US Department of Energy 2018 target set for platinum-group metal-free catalysts (PGM-free catalysts) in proton exchange membrane fuel cells, the low density of active sites must be overcome. Here, we report a class of concave Fe–N–C single-atom catalysts possessing an enhanced external surface area and mesoporosity that meets the 2018 PGM-free catalyst activity target, and a current density of 0.047 A cm –2 at 0.88 V iR-free under 1.0 bar H 2 –O 2 . This performance stems from the high density of active sites, which is realized through exposing inaccessible Fe–N 4 moieties (that is, increasing their utilization) and enhancing the mass transport of the catalyst layer. Further, we establish structure–property correlations that provide a route for designing highly efficient PGM-free catalysts for practical application, achieving a power density of 1.18 W cm −2 under 2.5 bar H 2 –O 2 , and an activity of 129 mA cm −2 at 0.8 V iR-free under 1.0 bar H 2 –air. Iron single-atom catalysts are among the most promising fuel cell cathode materials in acid electrolyte solution. Now, Shui, Xu and co-workers report concave-shaped Fe–N–C nanoparticles with increased availability of active sites and improved mass transport, meeting the US Department of Energy 2018 target for platinum-group metal-free fuel cell catalysts.