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Unitized regenerative fuel cells (URFCs) offer a cost‐effective solution for energy conversion by functioning as both fuel cells and electrolyzers. Anion‐exchange membrane‐based URFCs (AEM‐URFCs) require bifunctional electrocatalysts, such as Pt–Ir alloys, for the oxygen evolution reaction (water electrolysis mode) and oxygen reduction reaction (fuel cell mode). However, the low stability of Pt in alkaline media and the high cost of Ir remain challenges for the widespread application of these URFCs. In this study, a Pt–Ni octahedral alloy is synthesized to replace Ir with Ni as the oxygen evolution reaction catalyst. The alloying effect of Pt–Ni inhibits the dissolution of Pt and transforms PtOx to metallic Pt via a recovery process, thereby providing a new operational strategy for improving the durability of AEM‐URFCs. Remarkably, the performance of the AEM‐URFC single cell is maintained over ten cycles after the recovery process, demonstrating the viability of this approach for long‐term operations. These findings pave the way for broader applications and advancements of AEM‐URFCs. [ABSTRACT FROM AUTHOR]

Chemically-exfoliated graphene materials have been widely investigated for various applications. The graphene materials are typically synthesized from graphite granules, but their success as support materials of Fe-N-C electrocatalysts for the oxygen reduction reaction is highly ambiguous due to their large sheet-like morphology impeding the efficient transport of reactants/products. In this study, we synthesize a graphene-based Fe-N-C catalyst from cabon nanofibers as parent materials, which consist of stacked-cup carbon surrounded by a few graphitic walls. This Fe-N-C catalyst shows a much improved catalytic activity compared with that synthesized from graphite granules. The physical and electrochemical characterizations reveal that the carbon nanofibers are simultaneously transferred into a mixture of small graphene ribbons and flakes after chemical exfoliation and surface modification, forming a porous network structure in a fabricated electrode with a modified electronic structure. The electrocatalytic pathway, methanol-tolerance, and active site of the graphene-based Fe-N-C catalyst are also investigated. The results show that the carbon nanofibers are promising parent carbon materials for preparation of graphene-based Fe-N-C electrocatalysts. [ABSTRACT FROM AUTHOR]

Non-precious metal catalysts (typically Fe(Co)-N-C catalysts) have been widely investigated for use as cost-effective cathode materials in low temperature fuel cells. Despite the high oxygen reduction activity and methanol-tolerance of graphene-based Fe(Co)-N-C catalysts in an acidic medium, their use in direct methanol fuel cells (DMFCs) has not yet been successfully implemented, and only a few studies have investigated this topic. Herein, we synthesized a nano-sized graphene-derived Fe/Co-N-C catalyst by physical ball-milling and a subsequent chemical modification of the graphene oxide. Twelve membrane-electrode-assemblies are fabricated with various cathode compositions to determine the effects of the methanol concentration, ionomer ( i.e. Nafion) content, and catalyst loading on the DMFC performance. The results show that a graphene-based catalyst is capable of tolerating a highly-concentrated methanol feed up to 10.0 M. The optimized electrode composition has an ionomer content and catalyst loading of 66.7 wt% and 5.0 mg cm −2 , respectively. The highest maximum power density is ca. 32 mW cm −2 with a relatively low PtRu content (2 mg PtRu cm −2 ). This study overcomes the drawbacks of conventional graphene-based electrodes using a nano-sized graphene-based catalyst and further shows the feasibility of their potential applications in DMFC systems. [ABSTRACT FROM AUTHOR]

Fundamental understanding of non-precious metal catalysts for the oxygen reduction reaction (ORR) is the nub for the successful replacement of noble Pt in fuel cells and, therefore, of central importance for a technological breakthrough. Herein, the degradation mechanisms of a model high-performance Fe-N-C catalyst have been studied with online inductively coupled plasma mass spectrometry (ICP-MS) and differential electrochemical mass spectroscopy (DEMS) coupled to a modified scanning flow cell (SFC) system. We demonstrate that Fe leaching from iron particles occurs at low potential (<0.7 V) without a direct adverse effect on the ORR activity, while carbon oxidation occurs at high potential (>0.9 V) with a destruction of active sites such as FeN xC y species. Operando techniques combined with identical location-scanning transmission electron spectroscopy (IL-STEM) identify that the latter mechanism leads to a major ORR activity decay, depending on the upper potential limit and electrolyte temperature. Stable operando potential windows and operational strategies are suggested for avoiding degradation of Fe-N-C catalysts in acidic medium. [ABSTRACT FROM AUTHOR]

The electrochemical synthesis of hydrogen peroxide (H 2 O 2 ) represents a promising alternative to the anthraquinone process, as it combines on-site chemical and electrical production. The design of selective electrocatalysts is challenging and is commonly based on the alloying of elements to generate a synergistic effect and increase activity. In the present work, we report the electrochemical activity of Au-Pd nanoparticles immobilized directly onto an electrode as a model to study H 2 O 2 electrochemical synthesis from fundamentals to continuous production. The impact of composition on the oxygen reduction reaction (ORR), the selectivity, as well as the peroxide reduction and oxidation reactions (PROR) are studied. [ABSTRACT FROM AUTHOR]

• Surface of Me-N-C catalysts (Me = Co, Mn and Fe) was oxidized by H 2 O 2 treatment. • Oxidized Me-N-C catalysts promoted a 2e−-pathway in oxygen reduction reactions. • Dissociation of O O bond was suppressed by the introduced oxygen functionalities. • Among the three metal candidates, Co-N-C showed the highest H 2 O 2 selectivity. The electrochemical synthesis of hydrogen peroxide (H 2 O 2) can provide an attractive alternative to the current anthraquinone redox process, as it combines on-site chemical and electricity productions. A major challenge in the electrochemical H 2 O 2 synthesis is the catalyst design which leads to a selective two-electron pathway in the oxygen reduction reaction (ORR) without dissociation of the O O bond. In the present work, we report that the partial oxidation of metal-nitrogen-carbon catalysts (Me-N-C, Me = iron, cobalt and manganese) can modify their ORR mechanisms from a four- to a two-electron pathway. Spectroscopic measurements reveal that ex situ H 2 O 2 treatment introduces abundant oxygen functionalities on the Me-N-C surface without considerable changes to their bulk properties, such as crystallinity, degree of defects, surface area, and metal contents. Decreased H 2 O 2 reduction kinetics on the oxidized catalysts confirm that the dissociation of the O O bond is strongly suppressed by the newly introduced oxygen functionalities. Among the three central metal candidates, the cobalt-nitrogen-carbon catalyst shows the highest H 2 O 2 selectivity of >85%. This work provides a new simple guideline for designing Me-N-C catalysts for the efficient electrochemical synthesis of H 2 O 2. [ABSTRACT FROM AUTHOR]

• Fe-N-C catalyst was prepared for electrochemical oxygen reduction reactions. • Wetting with water and drying treatments introduced non-negligible activity loss. • Extend of the activity loss was affected by the treatment conditions. • Subtle changes in Fe-N-C surface were observed after the treatments. The membrane electrode assembly (MEA) is a core component of low-temperature fuel cells. The first step of MEA manufacturing is the preparation of a catalyst ink suspension in which the catalyst powder is homogeneously dispersed in a liquid solvent through mechanical or sonic agitation. In this work, we have studied the effects of catalyst dispersion in water or alcohol solutions and subsequent drying processes on the physicochemical properties of Fe-N-C catalysts and their electrocatalytic oxygen reduction activities. We find that dispersing the model Fe-N-C catalyst comprising only FeN x C y moieties in water and subsequent drying treatment change neither its bulk structure nor surface composition, as indicated by various spectroscopic measurements before and after treatment. However, zeta potential measurements, which are very sensitive to the chemistry of functionalities present on the carbon surface, reveal that the Fe-N-C catalyst becomes slightly more acidic, and that the change in their acido-basicity is magnified with a) increasing treatment temperature and b) repetitions of a same wetting/drying treatment. This small change in the surface acido-basicity of the Fe-N-C catalyst results in a measurable and reproducible decrease in its electrocatalytic activity, which shows a positive correlation with the zeta potential changes measured at pH = 1. Observed on the Fe-N-C catalyst but not on Pt/C, it is surmised that the electrocatalytic activities of the oxygen-reducing FeN x C y moieties are influenced by the surface chemistry of the carbonaceous support. Since catalyst wetting and drying processes are essential for MEA fabrication for fuel cells, these results suggest that careful attention should be paid to the conditions employed to prepare and dry catalytic inks for the family of Fe-N-C catalysts in order to obtain their highest possible ORR activity. [ABSTRACT FROM AUTHOR]

For polymer electrolyte membrane fuel cells (PEMFCs), the state-of-the-art electrocatalysts are based on carbon-supported Pt group metals. However, current carbon supports suffer from carbon corrosion during repeated start-stop operations, causing performance degradation. We report a new strategy to produce highly graphitized carbon with controllable N-doping that uses low-temperature synthesis (650 ℃) from g-C 3 N 4 carbon-nitrogen precursor with pyrolysis using Mg. The high graphiticity is confirmed by high-intensity 2D Raman peak with low I D /I G (0.57), pronounced graphitic XRD planes, and excellent conductivity. Without further post-treatment, this highly graphitized N-doped carbon (HGNC) material combines high pyrrolic-N content with high porosity. Supporting Pt on HGNC exhibits excellent oxygen reduction activity for PEMFC with greatly improved durability as proved by real-time loss measurements of Pt and carbon, the first to surpass the DOE 2025 durability targets for both catalyst and support. The Pt/HGNC-65 shows 32% and 24% drop in mass activity after accelerated durability tests of both electrocatalyst and support, respectively, which are less than DOE target of 40% loss. The atomistic basis for this durability is explained via quantum mechanics-based molecular dynamics simulations. Interestingly, it is found that pyrrolic-N strongly interacts with Pt, making the Pt catalyst more stable during fuel cell reaction. [Display omitted] • Highly graphitized N-doped carbon (HGNC) was prepared with Mg at 650 ℃. • The high graphiticity is confirmed by high-intensity 2D Raman with low I D /I G (0.57). • Predominant pyrrolic-N in Pt/HGNC improves the durability of active Pt during ORR. • The real-time loss measurements of both Pt and carbon confirm the improved durability. • Pt/HGNC surpassed the DOE 2025 durability targets for both Pt catalyst and support. [ABSTRACT FROM AUTHOR]

The focus in recent years is on developing high performance non-precious metal catalysts (NPMCs) to reduce the catalyst cost in fuel cells. However, little attention has been paid to improve the utilization of NPMCs. Thus, this study focuses on the optimization of electrode component, particularly the Nafion content. With the synthesized graphene based oxygen reduction reaction (ORR) catalyst, the catalyst inks were prepared at various Nafion contents with suitable amounts of catalysts sprayed on the gas diffusion media. Twenty different single cells were assembled and measured for polarization, resistance and electrochemical impedance. Electrodes of 66.7 and 50.0% Nafion contents showed the highest performance for hydrogen/oxygen and hydrogen/air operation, respectively. These results were explained using the electrochemical impedance spectra, where the highest performance electrode resulted with the lowest charge transfer resistance. Moreover, negligible change in performance was observed during the 80 h of stability test. The optimization compositions of NPMC-based MEAs were very different to Pt-based MEAs, indicating the importance of optimization studies for the practical use of NPMCs. [ABSTRACT FROM AUTHOR]