Atomic Fe in N‐doped carbon (FeNC) electrocatalysts for oxygen (O2) reduction at the cathode of proton exchange membrane fuel cells are the most promising alternative to platinum‐group‐metal catalysts. Despite recent progress on atomic FeNC O2 reduction, their controlled synthesis and stability for practical applications remain challenging. A two‐step synthesis approach has recently led to significant advances in terms of Fe‐loading and mass activity; however, the Fe utilization remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, this issue is addressed by coordinating Fe in a highly porous nitrogen‐doped carbon support (≈3295 m2 g−1), prepared by pyrolysis of inexpensive 2,4,6‐triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54 × 1019 sites gFeNC−1 and a record 52% FeNx electrochemical utilization based on in situ nitrite stripping are achieved. The Fe single atoms are characterized pre‐ and post‐electrochemical accelerated stress testing by aberration‐corrected high‐angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X‐ray absorption spectroscopy and low‐temperature Mössbauer spectroscopy suggest the presence of penta‐coordinated Fe sites, which are further studied by density functional theory calculations.

/pdf/fenc-oxygen-reduction-electrocatalyst-with-high-utilization-1twgm5ta.pdf

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites

Biomass derived diverse carbon nanostructure for electrocatalysis, energy conversion and storage

Exploring bio-inspired nanomaterials (BINMs) and incorporating them into micro/nanodevices represent a significant development in biomedical applications. Nanomaterials, engineered to imitate biological structures and processes, exhibit distinctive attributes such as exceptional biocompatibility, multifunctionality, and unparalleled versatility. The utilization of BINMs demonstrates significant potential in diverse domains of biomedical micro/nanodevices, encompassing biosensors, targeted drug delivery systems, and advanced tissue engineering constructs. This article thoroughly examines the development and distinctive attributes of various BINMs, including those originating from proteins, DNA, and biomimetic polymers. Significant attention is directed toward incorporating these entities into micro/nanodevices and the subsequent biomedical ramifications that arise. This review explores biomimicry’s structure–function correlations. Synthesis mosaics include bioprocesses, biomolecules, and natural structures. These nanomaterials’ interfaces use biomimetic functionalization and geometric adaptations, transforming drug delivery, nanobiosensing, bio-inspired organ-on-chip systems, cancer-on-chip models, wound healing dressing mats, and antimicrobial surfaces. It provides an in-depth analysis of the existing challenges and proposes prospective strategies to improve the efficiency, performance, and reliability of these devices. Furthermore, this study offers a forward-thinking viewpoint highlighting potential avenues for future exploration and advancement. The objective is to effectively utilize and maximize the application of BINMs in the progression of biomedical micro/nanodevices, thereby propelling this rapidly developing field toward its promising future.

Bio-Inspired Nanomaterials for Micro/Nanodevices: A New Era in Biomedical Applications

Abstract Biomass is a low-cost, abundant and renewable resource that can be used to manufacture porous carbon-based materials for a variety of applications. Different mesoporous carbon supports can be obtained from the various synthetic approaches that are aimed at increasing the specific surface area and functionalization. Currently, most of the biomass is used for energy recovery. The circular economy approach could lead to the development of cheap and sustainable materials, and turning of wastes into a precious resource. In this review, we provide the recent advances in the field of electrochemistry for porous carbon materials derived from biomass, which offers wider applications in proton exchange membrane fuel cells (PEMFCs), anion exchange membrane fuel cells (AEMFCs) and Zn-air batteries (ZABs). The focus is on understanding the required properties of the materials and the role of synthetic pathways in platinum group metal (PGM) free electrocatalysts. The most promising materials are evaluated towards the oxygen reduction reaction (ORR) in PEMFC, AEMFC, and ZAB. The results achieved showed that the expected performances on these energy conversion devices still lack for deployment in practice, especially if compared with commercially available PGM-free electrocatalysts. This review article provides insights on how to improve the actual electrocatalytic activity of biomass-derived materials. Graphical Abstract 

PGM-Free Biomass-Derived Electrocatalysts for Oxygen Reduction in Energy Conversion Devices: Promising Materials

Bio‐organisms with various architectures and versatile physiological functions provide a substantial bibliography for electrode design. To elucidate how bio‐organisms and bio‐schemes take effect in advanced electrode materials, this review sorts bio‐assisted construction into two categories, namely, biotemplating synthesis and biomimetic artificial fabrication. The former section summarizes unique characteristics of different biotemplates for electrode preparation, including “bottom‐up” structural designability of biomolecules, metabolism involving, and genetic alterable properties of biological cells, as well as, the structural regularity and integrity of bio‐tissues, with the aim to provide guidelines for manipulating bioarchitectures and endow biotemplating synthesis of electrodes with more designability. The later describes recent efforts in using bio‐prototypes to enhance the essential properties associated with advanced electrodes, including mechanical properties, wettability, mass transport, electron/charge transfer, and catalytic activity, with intensive concerns on the function principles of biomimetic designs in electrochemical systems. Then, advances in applications of bioderived and biomimetic electrode materials are summarized emphasizing how bio‐structures/components and bionic designs help to enhance the charging/discharging and electrocatalytic performance in specific electrochemical energy storage and conversion systems. Finally, future trends with prospects and challenges for developing new bioderived/biomimetic electrode materials, as well as, related conceptual innovation on bionics, are discussed in the last section.

Biologically Assisted Construction of Advanced Electrode Materials for Electrochemical Energy Storage and Conversion

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.

/pdf/bioinspired-and-bioderived-aqueous-electrocatalysis-254fg0ui.pdf

Bioinspired and Bioderived Aqueous Electrocatalysis

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...

Inducing Porosity in Xylose-derived FeNC Electrocatalysts for Alkaline Oxygen Reduction

Engineering macroporous carbon film supports for freestanding Fe-N-C cathodes at high current densities

Novel synthetic approaches have been developed to maximize the active site density of atomically dispersed Fe sites coordinated to nitrogen in carbon matrix. (Fe-N-C) (1,2) Nevertheless, the realistic maximum for single iron sites in these catalysts is deduced to be limited to 1021 sites per gram. (3) Therefore, for the application these Fe-N-C catalysts at the cathode for the oxygen reduction reaction in fuel cells, the catalyst material loading has to be increased to be able compete with the performance of Pt/C catalysts. Due to the resulting increased thickness of Fe-N-C catalyst layers, the oxygen available for the ORR at high current densities is dependent on the insufficient transport of oxygen across the catalyst layer. Freestanding catalyst nanostructured films, whose porosity is controlled across the entire thickness of the catalyst layer are expected to improve the mass transport at high current densities. Carbon nanostructures could provide the support substrate for such freestanding catalyst films. For instance, mesophase pitch-based films have been templated by silica (SiO2) nanoparticles have favourable morphologies for supporting Pt. (4) However, harsh conditions and long reaction times are required to etch away the SiO2. In our work, SiO2 nanoparticles are substituted by polystyrene nanoparticles, which decompose and tracelessly evaporate during the carbonization process. We have fabricated carbonized films of multiple thicknesses. We found 100 µm to be optimal, substantially thicker than Pt based electrodes to accommodate the lower density of sites and cheaper catalyst material. which is a usual thickness for Fe-N-C-based cathodes. Iron phthalocyanine (FePc) as a model active site is adsorbed on the freestanding carbon film. Gas-Diffusion-Electrodes (GDE) enable us to investigate the performance of such freestanding thin film catalysts at high current densities relevant for fuel cells. (5) A comparison of the ORR performance of catalyst layers, based on carbon films support (A) and conventional carbon particle support (B) are presented. We discuss the effect of adjusting the thickness of the two types of catalyst layers on the performance.
 1 Barrio J, Pedersen A, Feng J, Sarma S. C., Wang M, Li A. Y. , Luo, H. Ryan M. P., Titirici M.-M., Stephens I. E. L. J. Mater. Chem. A, 2022;10: 6023-30
 2 Mehmood A, Pampel J, Ali G, Ha H Y, Ruiz-Zepeda F, Fellinger T P Adv. Energy Mater., 2018; 8: 11649-55
 3 Mehmood A, Gong M, Jaouen F, Roy A, Zitolo A, Khan A, Sougrati M.-T., Primbs M., Martinez Bonastre A, Fongalland D, Drazic G, Strasser P, Kucernak A Nat. Cat., 2022;5, 311-23
 4 Atwa M, Li X, Wang Z, Dull S, Xu S, Tong X, Tang R, Nishihara H, Prinz F, Birss V 2021;8: 2451-62
 5 Inaba M, Jesen A W, Sievers G W, Escudero-Escribano M, Zana A, Arenz M Energy Environ. Sci,2018;11: 988-94

Macroporous Carbon Films Support Vs. Conventional Carbon Particles with FeN4 Sites for Oxygen Reduction in Gas-Diffusion-Electrodes

Influence of Commercial Ionomers and Membranes on a PGM-Free Catalyst in the Alkaline Oxygen Reduction

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