3.6 Elektrochemische Energiematerialien
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Paper des Monats
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Rising demand for sustainable energy storage has renewed interest in sodium-ion batteries (SIBs) as alternative to lithium-ion batteries. Although hard carbon and related materials are common SIB-anodes, the correlation between its structure and ion storage mechanism remains unclear.[1] As shown recently, the pore design is essential to block the formation of excessive solid electrolyte interphase (SEI) and allows the formation of pseudo-metallic clusters inside the pores.[2,3] Adjusting the diameter of the pore entrance, enables a reversible low-potential plateau (< 0.1 V), which significantly enhances the capacity (potentially up to 450-500 mAh/g) compared to graphite (Qtheo = 372 mAh/g) in Li-ion batteries.[2]
Activated carbon (AC) is a low-cost material with abundant micropores and high surface area, making it a promising anode candidate for SIBs. However, its performance is often hindered by structural disorder and excessive SEI-formation. Hence, mitigating active-species loss is essential to achieve high specific capacities (> 300 mAh g-1).[3] The aim herein was to investigate the relationship between the properties of the AC and the CVD-conditions required to achieve an efficient SIB-anode.
This study introduces an optimized chemical vapor deposition (CVD) method to modify various, highly porous commercial ACs aiming towards core-shell carbons, consisting of a porous core and a non-graphitic CVD-shell.[3] The ACs were treated via CVD and characterized using a range of techniques including gas physisorption, small-angle x-ray scattering and X-ray diffraction. The electrochemical properties of the different materials, prior and after CVD-coating, were analysed in half cells vs. Na-metal.
After coating, gas physisorption confirmed a significantly lower surface area for the materials. Depending on the porosity of the material, a longer CVD-time was necessary to fully coat the particles. The successful formation of core-shell carbons enables separation of the storage mechanism from SEI-formation. The CVD-process enables precise control over the microstructure of the carbon material, allowing to enhance the reversible Na-storage capacity, e.g., from 107 mAh g-1 to 353 mAh g-1 while significantly reducing initial Coulombic losses by 73%.
The greatly increased low-potential capacity verifies the formation of an electrolyte-tight CVD shell enabling Na-storage in the porosity of the core. The established link between porosity, CVD-parameters, and performance guides optimization for future materials.
Solid electrolytes (SE) allow to employ alkali-metal negative electrodes (NE) in new cell concepts, increasing energy density and safety of batteries for stationary and portable applications. The aim of this research is to develop a novel NASICON (NA Super Ionic CONductor) electrolyte for room-temperature (RT) sodium-sulfur (Na-S) cells employing a liquid sodium-potassium (Na-K) alloy at the SE/NE interface. The Na-K alloy can improve the interfacial contact between the sodium-metal NE and the SE.
Das Berlin Battery Lab (BBL) vereint exzellente Materialforschung, modernste Analytik und gezielten Technologietransfer. Als gemeinsames Labor von BAM, HZB und der Humboldt Universität zu Berlin entwickeln wir zukunftsfähige Natrium-Ionen- und Metall-Schwefel-Batterien – von der Materialidee bis zur funktionsfähigen Zelle.
Atomically dispersed Fe in N-doped carbon (Fe-N-C) catalysts are leading platinum-group-metal-free candidates for the O2 reduction reaction in proton exchange membrane fuel cells (PEMFCs). Zeolitic imidazolate framework (ZIF-8) derived Fe-N-C present the most promising performance; however, they possess a narrow distribution of small micropores, which limits active site accessibility. Here, to induce hierarchical porosity in Fe-N-C, we report a systematic study on MgCl₂·6H₂O-templated ZIF-8-derived Fe-N-C catalysts for the O2 reduction reaction. MgCl₂·6H₂O addition induced complete Zn removal, collapse of the ZIF-8 framework, and formation of large micro- and mesopores, with graphene-like structures. N content was markedly reduced, with conversion from pyridinic to pyrrolic N species. Rotating disc electrode tests showed a progressive increase in O2 reduction activity with MgCl₂·6H₂O, which is strongly correlated (R2 = 0.98) to the formation of large micropores and small mesopores (1-4 nm). This introduces a clear structure-activity design principle for Fe-N-Cs. The enhanced Fe-N-C porosity also leads to increased degradation rates under accelerated stress test conditions, which we attributed to the oxidation of disordered carbon domains and active Fe loss. This study highlights a key trade-off between porosity-driven O2 reduction activity and durability in Fe-N-C catalysts.
This cover illustrates the electrosynthesis of ammonia through the reduction of nitrate ions on metallic clusters formed from single atom catalysts. The artwork highlights the catalytic interface where molecular transformations occur, linking nanoscale reactions to sustainable fertilizer production. By converting pollutants into value-added products, this work envisions a green pathway toward circular nitrogen management and enhanced agricultural sustainability. More details can be found in the Research Article (DOI: 10.1002/advs.202510282) by Maria-Magdalena Titirici, Raphael Nagao, and co-workers.
The decoupled synthesis of Fe-NC single-site electrocatalysts mediated by Lewis acids enables high active site density and utilization. However, current approaches often rely on small organic molecules and suffer from low synthesis yields due to the high Lewis acid-to-precursor ratios required to achieve highly porous carbons. Here, a porous organic polymer (POP) based on 2,4,6-Triaminopyrimidine (TAP) is utilized as a carbon-nitrogen-based scaffold for the synthesis of Fe─NC electrocatalysts. By tuning the amounts of MgCl2 ·6H2O used both as porogen and active site templating agent, synthetic yields exceeding 45% are achieved, a significant improvement compared to the 6% yield from the molecular analogue and the highest reported forMg2+ templated systems. Subsequent low-temperature exchange with Fe leads to atomically dispersed FeNx, minimizing Fe aggregation. The resulting materials exhibit high specific surface areas (>1000 m2 g−1) with micro-, meso-, and macropores, which promote mass transport and active site accessibility. Compared to Fe─NC synthesized via direct pyrolysis of Fe-coordinated POP, the decoupled method enables significantly higher catalytic activity in both alkaline and acidic media, and delivers 1 A cm−2 at 0.687 ± 0.004 VRHE in an alkaline gas diffusion electrode, highlighting its potential for practical oxygen reduction devices.
理论模拟与实验协同的材料表征与机理研究
(2025)
In this academic salon among Chinese-speaking researchers within Germany and EU, I presented my work on utilizing computational chemistry to support experimental characterization and mechanism studies. The discussion focused on metal- and nitrogen-doped carbon (M-N-Cs) with well-defined coordination geometry as an excellent reference material for synergistic theory-experimental research. Some key topics included the analysis of structural preferences of imprinting ions, spectroscopic characterization of specific active sites and mechanism studies pertaining oxygen reduction reaction and hydrogen peroxide chemistry at these active sites.
A water-free ionothermal synthesis of porous magnesium-imprinted nitrogen-doped carbon (Mg–NC) materials is introduced to prepare a platform material to investigate electrocatalytic structure-performance relations. Atomically dispersed Co- and Fe-NCs isomorphic to the pristine Mg-NCs are prepared by ion-exchange reactions. The current Mg-templating strategy enables relatively high pyrolysis product yields of up to 50 wt% and resultant Fe-NC and Co-NC catalysts contain high and comparable active metal loading of up to 2.52 wt% Fe and 2.29 wt% Co, respectively. A combination of X-ray spectroscopies with DFT studies reveals a tetrapyrrolic structure of the coordination sites, originating from a pyrolytic magnesium template ion reaction within the ionothermal synthesis. Two sets of highly active isomorphic tetrapyrrolic Fe-NCs and Co-NCs are utilized to understand the differences in intrinsic electrocatalytic performance of Co-NCs and Fe-NCs towards the alkaline oxygen reduction reaction (ORR). Despite their superior valence electronic properties to facilitate the initial outer-sphere electron transfer to O2, Co-NCs show significantly lower performance than Fe-NC with comparable loading. Although the generally discussed weaker binding of peroxide intermediates to CoN4 sites compared to FeN4 sites is evident, experimental and theoretical investigation reveal that it is the underlying peroxide oxidation activity that suppresses the oxygen reduction activity of M-NCs. The high peroxide oxidation activity of Co-NCs explains their reduced alkaline ORR relative to Fe-NCs, shedding light on the understated significance of controlling peroxide chemistry for the optimizing cathodic performance.
Elucidating the Intrinsic CO2RR performance at MN4 sites using Morphologically Comparable M-N-Cs
(2025)
Metal- and nitrogen-doped carbons (M-N-Cs) are a promising class of low-cost electrocatalysts derived from earth-abundant elements for various electrochemical applications including ORR and CO2RR [1,2]. Traditionally, M-N-Cs containing active metals (M = Fe, Co, and Ni) are synthesized through direct pyrolysis of inorganic and organic precursors. However, this process often leads to the undesired formation of inorganic side phases via carbothermal reduction, hindering both the efficient incorporation of active metal and the intrinsic activity comparison among active sites.
To overcome these challenges, we developed an active-site imprinting strategy where active metals are introduced post-pyrolysis through ion-exchange [3-5]. In this work, we applied a Mg imprinting strategy to synthesize Co-N-Cs and Ni-N-Cs with comparable morphology and metal dopant concentrations, enabling a more direct comparison of their intrinsic activities. Notably, Ni-N-Cs produced via this method consistently demonstrated superior activity and selectivity compared to isomorphic Co-N-Cs, achieving CO Faraday efficiencies of up to 95% at relatively low overpotentials. Furthermore, the Ni-N-C catalyst exhibited excellent stability at -0.65 VRHE, retaining 92.5% of its current density and 97.6% of its CO selectivity after 100 hours of continuous operation.
A distinct advantage of the imprinting strategy lies in the suppression of inorganic side phases, enabling an accurate local structure characterization of the porphyrin-like tetrapyrrolic MN4 coordination structure using Extended X-ray Absorption Fine Structure (EXAFS). The characterization of the tetrapyrrolic NiN4 site is especially puzzling, as density functional theory (DFT) simulations often predict these sites to be inert to both CO2RR and HER. Drawing on recent studies which highlight the crucial role of cations for CO2RR on noble metal catalysts like Cu, Ag and Au [6-7], we performed mechanistic investigations using DFT to extend the relevance of cations to the CO2RR/HER performance at the MN4 sites, and further illustrate the advantage of the pyrrolic N atoms in anchoring them near the active metals.
Metal-and nitrogen-doped carbons (MN-Cs) represent a promising class of low cost electrocatalysts derived from nature-abundant elements for various electrochemical processes including CO 2 RR [1, 2]. Traditionally, MN-Cs containing active metals (M= Fe, Co, Ni) are synthesized by direct pyrolysis of inorganic and organic precursors, a process that often results in the undesired formation of inorganic side phases through carbothermal reduction, impeding the effective integration of active metals like Fe, Co and Ni. Furthermore, comparing the intrinsic activities of different MN-Cs can be complicated due to variations in catalyst morphology and active site concentration that arise during the pyrolysis.
To address these challenges, we developed an active-site imprinting strategy in which active metals are introduced post-pyrolysis via ion-exchange [3-5]. In this work, we employed the Mg imprinting strategy to produce Co-N-Cs and Ni-N-Cs with comparable morphology and metal dopant concentration. Our approach allows for a more direct comparison of the intrinsic activities that arise from the metal dopant. The Ni-N-Cs derived this way are consistently higher in activity and selectivity than the corresponding Co-N-Cs, exhibiting a CO Faraday efficiency of up to 95% at potentials between-0.5 to-0.8 V RHE. The Ni-NC catalyst maintains high stability at-0.65 V RHE, with 92.5% retention of current density and 97.6% retention of CO selectivity after 100 hours of continuous operation.