Key Takeaways & Executive Findings
- •• • Fe−N−PCG achieves a site density (SD) of 2.74×10^19 sites g−1 and Fe utilization (UFe) of 51.7%, significantly enhancing active site exposure compared to conventional Fe−N−C catalysts, which typically suffer from buried sites and utilization below 20%. This directly translates to higher volumetric activity and reduced catalyst loading in practical devices. • • In a half-cell configuration, Fe−N−PCG exhibits a mass transport overpotential (ηmt) of only 67 mV at 800 mA cm−2, demonstrating superior mass transport efficiency under high current densities where conventional catalysts are limited by diffusion. This enables operation at industrially relevant current densities without excessive voltage loss. • • Zinc-air battery tests show Fe−N−PCG delivers a peak power density of 296.1 mW cm−2 at 500 mA cm−2, exceeding Pt/C (241 mW cm−2 at 438 mA cm−2) and control samples (Fe−N−CG: 283 mW cm−2, Fe−N−PG: 255 mW cm−2, Fe−N−G: 239 mW cm−2). This high power density is critical for high-rate applications such as electric vehicles and grid storage. • • At a galvanostatic discharge of 50 mA cm−2, Fe−N−PCG provides a specific capacity of 815 mAh g−1 and a discharge voltage of 1.19 V, outperforming Pt/C (715 mAh g−1, 1.13 V). The higher capacity and voltage under load indicate improved energy efficiency and longer operational lifetime, essential for commercial viability.
Abstract
The sluggish kinetics of the oxygen reduction reaction (ORR) necessitates platinum-based catalysts, but their high cost and scarcity drive the search for platinum-group metal-free (PGM-free) alternatives. Fe−N−C catalysts with atomically dispersed Fe−N4 sites are promising, yet their practical performance is limited by buried active sites and poor mass transport. Here, a crumpled, multi-scale porous Fe−N−C catalyst (Fe−N−PCG) is synthesized via spray pyrolysis coupled with high-temperature metal etching. The crumpled morphology, formed by capillary compression during rapid solvent evaporation, and in-plane mesopores from Fe nanoparticle etching, synergistically enhance site accessibility and mass transport. Fe−N−PCG achieves a site density (SD) of 2.74×10^19 sites g−1 and Fe utilization (UFe) of 51.7%. As a gas diffusion electrode, it delivers a mass transport overpotential (ηmt) of 67 mV at 800 mA cm−2. In zinc-air batteries, Fe−N−PCG exhibits a peak power density of 296.1 mW cm−2 at 500 mA cm−2, outperforming Pt/C (241 mW cm−2 at 438 mA cm−2). At 50 mA cm−2, it delivers a discharge voltage of 1.19 V and a specific capacity of 815 mAh g−1, surpassing Pt/C (1.13 V, 715 mAh g−1). These results demonstrate that morphology and porosity engineering can concurrently optimize intrinsic activity, site utilization, and mass transport, offering a rational design strategy for high-performance PGM-free catalysts.
1. Introduction
The commercial deployment of electrochemical energy conversion devices, including fuel cells and metal-air batteries, is constrained by the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. Platinum-based catalysts remain the benchmark for overcoming this kinetic barrier, but their prohibitive cost and limited supply impede widespread adoption. Iron-nitrogen-carbon (Fe−N−C) materials with atomically dispersed Fe−N4 moieties have emerged as the most promising platinum-group metal-free (PGM-free) alternatives, offering comparable activity at a fraction of the cost. However, the practical performance of Fe−N−C catalysts is severely limited by the inaccessibility of active sites buried within the carbon matrix and by mass transport limitations under high current densities. These issues result in low site utilization and premature performance degradation, particularly in high-power applications.
To address these bottlenecks, this work introduces a crumpled, multi-scale porous Fe−N−C catalyst (Fe−N−PCG) synthesized via spray pyrolysis combined with high-temperature metal etching. The crumpled morphology, induced by capillary compression during rapid solvent evaporation, and the in-plane mesopores generated by etching of Fe nanoparticles, collectively create abundant triple-phase boundaries. This architecture enhances both the exposure of Fe−N4 sites and the diffusion of reactants and products. The resulting catalyst achieves a site density of 2.74×10^19 sites g−1 and Fe utilization of 51.7%, while delivering a mass transport overpotential of only 67 mV at 800 mA cm−2. In zinc-air batteries, Fe−N−PCG outperforms Pt/C, achieving a peak power density of 296.1 mW cm−2 and a specific capacity of 815 mAh g−1 at 50 mA cm−2. These results demonstrate a viable pathway for designing PGM-free catalysts that simultaneously optimize intrinsic activity, site accessibility, and mass transport.
Loading authentic research manuscript (Pages 1–5)...
HE Guanchao, LIU Jingjing, YAN Minmin, LIU Jianbin, LU Zhixiu, YOUNUS Hussein A., YE Gonglan, FEI Huilong (2026). Crumpled and Multi-Scale Porous Fe−N−C Catalyst with Enhanced Site Accessibility and Mass Transport in Oxygen Reduction. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4371-6
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the long-term stability of Fe−N−PCG under high current density operation, and what degradation mechanisms are observed?
The provided text does not include long-term stability data. However, the high site utilization and mass transport efficiency suggest improved robustness compared to conventional Fe−N−C catalysts. In zinc-air battery tests, Fe−N−PCG delivered stable discharge voltages at current densities up to 200 mA cm−2, but degradation rates over extended cycling are not reported. Future studies should assess Fe dissolution, carbon corrosion, and pore structure evolution under prolonged operation.
How does the cost of Fe−N−PCG compare to Pt/C on a per-kilowatt basis, considering precursor and processing costs?
The synthesis employs earth-abundant iron salts, nitrogen precursors, and carbon sources, with spray pyrolysis and acid etching as scalable processes. While precise cost analysis is not provided, the elimination of platinum and the use of inexpensive precursors suggest a significant cost advantage. However, the high-temperature etching step and acid washing may add processing costs. A detailed techno-economic assessment is required to confirm parity with Pt/C.
What are the scalability challenges for producing Fe−N−PCG in industrial quantities, particularly regarding the spray pyrolysis and etching steps?
Spray pyrolysis is a continuous, scalable technique already used in industry for carbon black and battery materials. The high-temperature etching of Fe nanoparticles requires precise control of temperature and atmosphere to ensure uniform pore formation. Acid washing to remove residual Fe must be optimized for waste treatment and cost. The process is amenable to roll-to-roll production, but pilot-scale validation is needed to confirm batch-to-batch consistency and yield.
How does the multi-scale porous structure of Fe−N−PCG affect water management and flooding in practical fuel cells or zinc-air batteries?
The macropores within the crumpled graphene balls facilitate rapid gas diffusion and water removal, while in-plane mesopores provide access to active sites. This hierarchical porosity mitigates flooding by preventing water accumulation in micropores. In zinc-air battery tests, Fe−N−PCG maintained high discharge voltages at 200 mA cm−2, indicating effective water management. However, long-term flooding resistance under varying humidity and current profiles requires further investigation.
What is the tolerance of Fe−N−PCG to impurities such as sulfur and chloride, which are common in practical air streams?
The text does not report impurity tolerance. Fe−N−C catalysts are generally susceptible to poisoning by sulfur and chloride, which can block active sites or alter Fe coordination. For practical applications, the catalyst must withstand typical air impurities. Future work should include accelerated stress tests with SO2, NOx, and Cl− to evaluate robustness and identify mitigation strategies.
Related Chinese Research & Cross-Citations
Ammonium Vanadate Cathodes in Aqueous Zinc-Ion Batteries: Design Strategies and Research Progress
Aqueous zinc-ion batteries (AZIBs) offer a compelling combination of high safety, environmental compatibility, and abundant zinc resources, positioning them as viable candidates for grid-scale energy storage. Their practical deployment, however, is constrained by cathode materials that suffer from structural degradation, sluggish Zn2+ diffusion, and inadequate electronic conductivity. Ammonium vanadates (AVOs) have emerged as high-performance cathodes owing to their layered or tunneled frameworks, which accommodate reversible Zn2+ (de)intercalation with diffusion coefficients superior to conventional vanadium oxides. This review systematically examines recent advances in AVO cathodes for AZIBs, correlating morphological variations—including nanowires, nanobelts, and microflowers—with electrochemical characteristics. The analysis establishes structure–performance relationships that govern capacity retention, rate capability, and cycling stability. Key optimization strategies are critically assessed: defect engineering to enhance electronic conductivity and active site density, interlayer spacing modulation via pre-intercalated cations or structural water to facilitate Zn2+ transport, and composite construction with conductive carbonaceous or polymeric matrices to mitigate dissolution and improve mechanical integrity. Despite these advances, challenges persist in achieving long-term cycling stability (>10,000 cycles) and high areal mass loading (>10 mg cm-2) required for commercial viability. The review concludes by outlining future research directions, including operando characterization of degradation mechanisms and scalable synthesis routes for AVO cathodes in practical AZIB configurations.
Microenvironment-responsive therapeutic platforms: Innovations for spinal cord injury repair
Spinal cord injury (SCI) remains a formidable clinical challenge due to the complex, dynamic lesion microenvironment that impedes axonal regeneration and functional recovery. This highlight examines a microenvironment-responsive therapeutic platform integrating microneedle delivery, ferroptosis modulation, and hydrogen therapy. The platform leverages the pathological hallmarks of SCI—oxidative stress, iron dyshomeostasis, and lipid peroxidation—to achieve spatiotemporally controlled cargo release. By combining microneedle arrays for minimally invasive intraparenchymal administration with hydrogen-releasing biomaterials, the system addresses the dual bottlenecks of poor drug penetration across the blood-spinal cord barrier and insufficient neutralization of reactive oxygen species. Ferroptosis inhibition is achieved through iron chelation and glutathione peroxidase 4 (GPX4) stabilization, while hydrogen gas scavenges hydroxyl radicals and peroxynitrite. This multimodal strategy attenuates secondary injury cascades, reduces glial scar formation, and promotes neural stem cell differentiation. The work is supported by the National Natural Science Foundation of China (82574518) and the Talent Cultivation Project of Paring Academicians with Young Talents in higher education institutions in Zhejiang. The authors declare no conflict of interest. This highlight underscores the translational potential of microenvironment-responsive platforms for SCI repair, emphasizing the need for rigorous preclinical validation and scalable manufacturing.
Dual-Site Adsorption over Phosphorus-Doped Copper Oxide for Efficient CO2 Electroreduction to Ethylene
Electroreduction of CO2 to ethylene offers a promising route for renewable electricity storage, yet achieving high ethylene selectivity at industrial current densities remains challenging due to the large energy barrier for C–C coupling. Here, we report a “MOF-assisted in situ doping” strategy to introduce the oxophilic nonmetal phosphorus (P) into the copper oxide (CuO) lattice, constructing a localized Cu–P dual-site adsorption configuration for the key *OCCHO intermediate. The optimized catalyst delivers an impressive Faradaic efficiency of 64.6% for ethylene with a partial current density of 646 mA cm-2. Comprehensive structural characterizations demonstrate that P mainly occupies Cu sites, generating abundant lattice defects and oxygen vacancies. In situ synchrotron infrared spectroscopy and theoretical calculations reveal that P doping modulates the electronic structure of Cu, optimizes the binding energies of *CO and *CHO, and stabilizes *OCCHO via P–O/Cu–C dual-site adsorption, thereby significantly lowering the asymmetric C-C coupling energy barrier to 0.74 eV. This work highlights a dual-site microenvironment regulation strategy for CO2-to-ethylene electroreduction.
Hydrophilic Single-Atom Interface Unlocks Low-Potential CO Removal on Pt in PEMFCs
Proton exchange membrane fuel cells (PEMFCs) fed with reformate hydrogen suffer severe anode poisoning by trace CO, necessitating high CO electrooxidation potentials that degrade performance and durability. This work introduces a Pt@CrSA-N-C anode catalyst featuring a hydrophilic Cr single-atom interface that simultaneously weakens CO adsorption on Pt via electronic regulation and promotes water activation, thereby lowering the CO oxidation onset potential to approximately 0.13 V vs. RHE. The onset potential was determined by two independent methods: the first potential at which the background-corrected current exceeds 0 mA cm-2 during CO oxidation reaction tests in a three-electrode system, and the potential at which the forward scan current exceeds the N2 background current in CO-stripping voltammetry. The catalyst achieves a maximum power density under 100 ppm CO that surpasses reported advanced catalysts, as compiled in Table S5. Structural, spectroscopic, and electrochemical characterizations collectively establish a coherent rationale for the hydrophilic single-atom interface strategy. This approach addresses the longstanding trade-off between CO tolerance and Pt utilization, offering a viable route for low-potential CO removal in practical PEMFC anodes.
An Ionoelastomer-Based Bioinspired Wearable Electronics with Tele-Perception and Tactile Sensation for Machine Learning-Assisted Rehabilitation Management
Comprehensive assessment of rehabilitation efficiency is essential for designing appropriate training programs for better musculoskeletal functional recovery. Existing contact-receptor-dependent rehabilitation assessment systems mostly focus on assessing the restoration of muscle function by evaluating grip strength or joint flexion angle; however, parameters reflecting neuromuscular synergistic function are always overlooked. Herein, we develop an ionoelastomer-based soft artificial electroreceptor (SAER) that integrates tele-perception and tactile sensation to track the rehabilitation process, collecting signals related to approaching speed and grip strength sequentially. The SAER uses polyurethane ionoelastomer incorporated with quasi-solid conductive salt as the electric field receptor, and is integrated on a rehabilitation-training ball after assembly to establish an untethered detection device; this enables the remote capture of hand approaching parameter within a 9 cm range, followed by the quantification of grip strength when contacting and grasping. Furthermore, a data-driven assessment system is established by integrating machine learning, which accurately classifies rehabilitation efficiency into six levels; it supports for rehabilitation evaluation and training programs adjustment. Overall, the SAER-based rehabilitation management system establishes a paradigm that synergistically evaluating parameters corresponding to neuromuscular functional restoration and holds strong potential for home-based active rehabilitation for minimizing dependence on frequent clinical supervision.
Microwave-Absorbing Materials with Strong Environmental Adaptability for Corrosion Protection, Anti-Icing, and Thermal Management
Microwave-absorbing materials (MAMs) deployed on naval vessels, aerospace vehicles, and critical electronic systems face coupled electromagnetic, marine salt-spray corrosion, and extreme-temperature loads that legacy single-function absorbers cannot withstand. This review consolidates progress on three environmentally adaptive MAM classes: corrosion-protective, anti-icing, and thermal-management absorbers. The electromagnetic loss and impedance-matching fundamentals are first established, then the synergistic mechanisms, design strategies, and characterization protocols for each class are examined against representative material systems and their measured performance. The analysis identifies a shared design logic—multiscale hierarchical architecture, interfacial polarization engineering, and multifunctional phase integration—while distinguishing the divergent protection mechanisms: barrier and passivation effects for corrosion, surface-energy and latent-heat regulation for anti-icing, and phonon–electron transport decoupling for thermal management. Persistent bottlenecks include the trade-off between impedance matching and protective-layer density, the absence of standardized coupled-field test protocols, and the scarcity of long-term salt-spray and thermal-cycling durability data. Future directions are delineated: intelligent self-adaptive absorbers, multiphysics-coupled simulation frameworks, and environmentally benign multifunctional integration. The review provides a theoretical and technical basis for the design, construction, and engineering scale-up of next-generation high-performance absorbers for aerospace, electronic, and marine equipment.