Heterogeneous catalysts consisting of iron cations incorporated into nitrogen-doped carbon (“Fe-N-C”) have received extensive attention as leading alternatives to Pt for the electrochemical oxygen reduction reaction (ORR). Fe-N-C catalysts host mononuclear nitrogen-ligated active centers, FeN x , that frequently coexist with agglomerated Fe species. Although FeN x are the dominant active centers for ORR and other electrocatalytic reactions, the relative accuracies of methods to quantify them are still debated. Here, we develop a kinetic probe-reaction approach to quantify FeN x centers and compare it with spectroscopic and molecular probe methods. Model Fe-N-C catalysts were synthesized to contain mononuclear FeN x species at low loadings (0.1–0.4 wt% bulk Fe) on solvent-accessible surfaces using a postsynthetic metalation approach and their Fe speciation was confirmed by low-temperature 57 Fe Mössbauer spectroscopy. The initial rate of oxidation of a water-soluble hydroquinone molecule (per g catalyst ) catalyzed by these model materials correlates linearly with their density of FeN x centers, reflecting their intrinsic turnover frequency (TOF) for this reaction. This TOF, in turn, enables the estimation of the active-site density on any other Fe-N-C catalyst through a simple rate measurement. Kinetically determined FeN x site densities are measured on a suite of fourteen Fe-N-C catalysts with diverse synthetic origins and Fe speciation (0.3–8.4 wt% bulk Fe) and are compared with those estimated by low-temperature 57 Fe Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical stripping of NO derived from NO 2 − . Kinetic quantifications of FeN x centers correlate well with those obtained from the CO pulse chemisorption method and Mössbauer spectroscopy. The broad survey of Fe-N-C materials also reveals the presence of outliers and challenges associated with each site quantification method. The kinetic method developed here does not require pretreatments that may alter active-site distributions nor specialized equipment beyond reaction vessels and standard analytical instrumentation, offering an attractive complementary approach. Figure 1

The stability of Fe−N−C oxygen reduction reaction (ORR) electrocatalysts has been considered a primary challenge for their practical application in proton exchange membrane fuel cells (PEMFCs). While several studies have attempted to reveal the possible degradation mechanism of Fe−N−C ORR catalysts, there are few research results reporting on their stability as well as the possible Fe species formed under different voltages in real PEMFC operation. In this work, we employ in‐situ X‐ray absorption near‐edge structure (XANES) to monitor the active‐site degradation byproducts of an atomically dispersed Fe−N−C ORR catalyst under a H2/O2‐operating PEMFC at 90 % relative humidity and 80 °C. For this, stability tests were carried out at two constant cell voltages, namely 0.4 and at 0.8 V. Even though the ORR activity of the Fe−N−C catalyst decreased significantly and was almost identical at the end of the tests for the two voltages employed, the analysis of the XANES recorded under H2/N2 configuration at 0.6 and 0.9 V within the stability test suggests that two different degradation mechanisms occur. They are demetalation of iron cations followed by their precipitation into Fe oxides upon operation at 0.8 V, versus a chemical carbon oxidation close to the active sites, likely triggered by reactive oxygen species (ROS) originated from the H2O2 formation, during the operation at 0.4 V.

Developing sustainable synthesis processes is a primary objective for the chemical industry since harsh process conditions and usage of fossil resources increase greenhouse gas emissions and the carbon footprint. Making use of CO2 as a feedstock to produce value-added organic chemicals is an attractive opportunity to realize a circular carbon economy. Moreover, electric energy generated by solar panels or wind power stations could be saved in stable chemical products. We combined both aspects in a novel bio-electrochemical system (BES) in which a PEM electrolysis cell is coupled to a standard stirred tank bioreactor. Precious group metal-free (PGM-free) catalysts consisting of atomically dispersed active metal sites in nitrogen-doped porous carbon matrix (M-N-C where M= Co, Ni, Zn etc.) enabled electrocatalytical CO2 reduction to CO (CO2RR) in an aqueous environment. The acetogenic bacterium Clostridium ragsdalei directly converts the CO into organic acids and alcohols. Besides, the competing hydrogen evolution reaction (HER) delivers H2 as an additional electron carrier that can be consumed together with CO2. Bacteria are more flexible towards the stoichiometry of their substrates (CO, H2 and CO2), demonstrating an advantage over chemical synthesis processes that often require exact stoichiometries. Further, mild process conditions in bioprocesses allow for more sustainable production. The BES consists of a stirred-tank bioreactor adapted to function together with an electrolysis cell. The cathode and anode are stacked in a membrane-electrode-assembly (MEA) mounted at the bottom with the cathode facing the bioreactor (Figure 1). The fully controlled BES is continuously gassed with CO2 and driven in a potentiostatic mode. A Zn/Co-N-C catalyst coated on carbon support was selective for the CO2 reduction to CO (Schwarz et al., 2024). CO and H2 were continuously produced at the cathode in an applied cell voltage range of -2.2 to -3.2 V. At lower applied voltages (≤ -2.5 V), the catalyst was more selective towards CO formation, whereas a higher cell voltage of -3.2 V caused the HER to take over the CO2RR. During electrofermentations, the cell voltage was increased stepwise to supply sufficient carbon and electron sources to C. ragsdalei. The MEA construction was modified continuously to improve autotrophic batch electrofermentations with C. ragsdalei. Optimizing the compression between the cathode and anode improved the stability of current flows and prolonged the total process time from 3 to 6 days. Increasing the initially low area-to-volume ratio of the cathode with the electrocatalyst (0.0012 cm-1) allowed a higher CO formation rate. CO generation has been limiting the whole electrocatalytical CO2 fermentation process. Furthermore, developing more selective and stable electrocatalysts towards the CO2RR improved the faradaic efficiency. Switching from a two-electrode to a three-electrode setup enabled a more precisely controlled galvanostatic operation with defined CO formation rates sufficient for C. ragsdalei to grow and produce acetate and ethanol in considerable amounts. Reference Schwarz I, Rieck A, Mehmood A, Bublitz R, Bongers L, Weuster-Botz D, Fellinger T-P (2024): PEM electrolysis in a stirred-tank bioreactor enables autotrophic growth of Clostridium ragsdalei with CO2 and electrons. ChemElectroChem 11: e202300344. Acknowledgements Funding by the German Research Foundation (DFG) within the framework of the priority program SPP 2240 (research projects WE 2715/17-1 and FE 1590/1-1) is gratefully acknowledged. Figure 1

The degradation of a single-site atomically dispersed, model Fe-N-C powder catalyst with high activity is investigated using cryo-Mössbauer spectroscopy. The results indicate a degradation initiated by an Fe2+ to Fe3+ oxidation due to coordination of oxygen to tetrapyrrolic Fe-N4 sites at atmospheric conditions (change between characteristic doublets) before iron(III) oxide is formed (sextet). Thermal reactivation can be used to restore substantial catalytic activity of aged Fe-N-C powders.

Non-precious Fe-N-C catalysts have reached high activity levels for acidic oxygen reduction reaction (ORR) in rotating ring disk electrode (RRDE) setup approaching to that of the platinum group metals (PGM) when compared at high catalyst loadings of 0.6-1.0 mgFe-N-C cm-2. The improvements in the ORR activity of Fe-N-Cs can be attributed to new synthetic routes developed in recent years that have led to increased Fe-N4 active site density and utilization and/or better intrinsic activity/turnover frequency (TOF) of those sites.1-3 Despite impressive activities in half-cells, Fe-N-Cs still require quite high loadings in the range of 4.0-5.0 mg cm-2 in proton exchange membrane fuel cells (PEMFCs), which makes the Fe-N-C cathodes 4-5x thicker than Pt-based cathodes (~100 µm for Fe-N-C layer vs ~10-20 µm for Pt layer). Thick Fe-N-C cathodes suffer from quick performance drop in medium to high current density region due to mass-transport related losses. Reducing the Fe-N-C loading levels in RRDE and in PEMFC without comprising the ORR activity would need further improvements in active site density, site utilization and TOF. In this talk, I will present our work on how morphological tailoring of carbon framework in Fe-N-Cs affects the utilization of active sites and water adsorption-desorption behaviour with the aim of improving the ORR performance and mass-transport properties. Active-site imprinted carbon frameworks are used to prepare Fe-N-Cs that consist of purely Fe-N4 sites without any other iron species.1,4,5 Besides activity, performance stability against extensive voltage cycling in RRDE and long-term durability in PEMFC single-cells is another important criterion that Fe-N-Cs need to fulfil for becoming a viable substitute to PGM catalysts. Very recently, encouraging results on the improvement of Fe-N-C durability in PEMFC tests have been reported using radical scavengers and by coating a thin carbon layer on the surface of Fe-N-C.6,7 However, significantly more efforts are required in that direction for reaching the durability targets of thousands of hours. Second part of the talk will discuss the performance stability of Fe-N-Cs. References 1. Mehmood, A. et al. High loading of single atomic iron sites in Fe-NC oxygen reduction catalysts for proton exchange membrane fuel cells. Nature Catalysis 5, 311-323 (2022). 2. Menga, D. et al. Resolving the Dilemma of Fe-N-C Catalysts by the Selective Synthesis of Tetrapyrrolic Active Sites via an Imprinting Strategy. J Am Chem Soc 143, 18010-18019 (2021). 3. Jiao, L. et al. Chemical vapour deposition of Fe-N-C oxygen reduction catalysts with full utilization of dense Fe-N(4) sites. Nat Mater 20, 1385-1391 (2021). 4. Menga, D. et al. Active-Site Imprinting: Preparation of Fe-N-C Catalysts from Zinc Ion-Templated Ionothermal Nitrogen-Doped Carbons. Advanced Energy Materials 9, 1902412 (2019). 5. Mehmood, A. et al. Facile metal coordination of active site imprinted nitrogen doped carbons for the conservative preparation of non‐noble metal oxygen reduction electrocatalysts. Advanced Energy Materials 8, 1701771 (2018). 6. Xie, H. et al. Ta–TiO x nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts. Nature Energy 7, 281-289 (2022). 7. Liu, S. et al. Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells. Nature Energy 7, 652-663 (2022).

Mononuclear Fe ions ligated by nitrogen (FeNx) dispersed on nitrogen-doped carbon (Fe-N-C) serve as active centers for electrocatalytic O2 reduction and thermocatalytic aerobic oxidations. Despite their promise as replacements for precious metals in a variety of practical applications, such as fuel cells, the discovery of new Fe-N-C catalysts has relied primarily on empirical approaches. In this context, the development of quantitative structure-reactivity relationships and benchmarking of catalysts prepared by different synthetic routes and by different laboratories would be facilitated by the broader adoption of methods to quantify atomically dispersed FeNx active centers. In this study, we develop a kinetic probe reaction method that uses the aerobic oxidation of a model hydroquinone substrate to quantify the density of FeNx centers in Fe-N-C catalysts. The kinetic method is compared with low-temperature Mössbauer spectroscopy, CO pulse chemisorption, and electrochemical reductive stripping of NO derived from NO2- on a suite of Fe-N-C catalysts prepared by diverse routes and featuring either the exclusive presence of Fe as FeNx sites or the coexistence of aggregated Fe species in addition to FeNx. The FeNx site densities derived from the kinetic method correlate well with those obtained from CO pulse chemisorption and Mössbauer spectroscopy. The broad survey of Fe-N-C materials also reveals the presence of outliers and challenges associated with each site quantification approach. The kinetic method developed here does not require pretreatments that may alter active-site distributions or specialized equipment beyond reaction vessels and standard analytical instrumentation.

Platinum-group-metal-free (PGM-free) catalysts are currently considered as potential oxygen-reduction-reaction (ORR) catalysts to replace costly and supply-limited platinum at the cathode side of proton exchange membrane fuel cells (PEMFCs). Extensive research efforts have led to substantial progress with regards to the ORR activity of PGM-free ORR catalysts, but there is uncertainty about the dependence of the mass activity on the catalyst loading. In this study, the effect of catalyst loading on the mass activity is investigated by means of rotating disk electrode measurements as well as single cell PEMFC tests using a commercial PGM-free ORR catalyst. Single cell tests with a wide range of loadings (0.4–4.0 mg cat cm −2 MEA ) are compared to rotating disk electrode measurements with low loadings of 40–600 μ g cat cm −2 disk . In contrast to indications in the literature that the ORR activity depends on catalyst loading, our results reveal an independence of the ORR mass activity from the catalysts loading in both RDE and PEMFC tests, if corrections for the voltage losses in H 2 /O 2 single cell tests are considered. Moreover, no clear relation of the stability to the catalyst loading was found in H 2 /O 2 PEMFCs.

Hard carbons with a disordered graphitic structure show promise as anode materials in next generation Na-ion batteries with stable and high sodiation/desodiation capacities. Since the mechanism of adsorption is not stoichiometric, as opposed to the case of Li-intercalation into graphite (LiC6), the search for an upper limit for the reversible capacity is an important task. We herein present a highly nanoporous nitrogen doped carbon obtained from ionothermal carbonization of a Zn-imidazolium framework that shows a stable cycling capacity of 496 mA h g(-1) at 30 mA g(-1) and 280 mA h g(-1) at 5 A g(-1) thus demonstrating exceptionally high capacity and outstanding rate performance. Although the reversible capacity was obtained only after extensive SEI formation, our results reveal the potential for much higher reversible capacities than usually observed today using carbons with a tailored porosity in Na-ion batteries. The electrochemical behavior is explained by improved utilization through a nanoscopic transport pore system and large graphitic interlayer distances. Initial SEI formation is herein used to passivate the carbon surface and obtain an ion-sieving coating. The ion sieving can allow for stable cycling at high capacity without further SEI formation because of a formed physical barrier between solvent molecules and metallic sodium.

Electrochemical impedance spectroscopy (EIS) is a powerful and non-invasive technique to gain valuable insights into the lithium or sodium intercalation kinetics via monitoring of the associated resistances.[1,2,3] To date, the measurement of symmetrical cells is the most commonly used approach to differentiate between the contributions of anode and cathode to the full-cell impedance. However, this method requires the reassembly of two identically treated anodes and cathodes from (aged) full-cells into a symmetric cell. Therefore, disassembly and reassembly of numerous cells is needed to perform state-of-charge (SOC) and/or state-of-life dependent EIS analyses. On the other hand, simultaneous in-situ measurement of the anode and cathode impedance can be achieved via incorporation of a micro-reference electrode (µ-RE) within the cell setup. Solchenbach et al. [4] and others [5] have shown such a µ-RE has to fulfill the following fundamental requirements: (a) its potential has to be stable within the measuring time of the impedance spectrum, (b) it has to be located centrally between anode and cathode, and (c) its cross-sectional dimensions have to be small compared to the distance between the electrodes. In this talk, we will introduce a novel micro-reference electrode for sodium-ion batteries based on an insulated tin wire with a diameter of ≈75 mm, further on referred to as Tin Wire Reference Electrode (TWRE), which is electrochemically alloyed with sodium after cell assembly from either the working or the counter electrode in order to receive a stable reference potential. This TWRE enables measuring the impedance response of sodium-based active materials in-situ during cycling. Since hard carbons (HCs) currently are the most promising candidates as anode materials for emerging sodium ion batteries (SIBs),[3,6] we will present data on the impedance evolution of a commercial HC anode as a function of SOC during sodiation and desodiation (see Figure 1). By comparing in-situ EIS data with impedance measurements performed using the symmetrical cell approach, we will prove that reliable impedance responses can be obtained in-situ. Figure 1a exemplary shows two in-situ impedance spectra of a HC anode in a Nyquist plot representation, one measured directly after cell assembly and sodiation of the tin wire (0% SOC, black) and the other measured after sodiation of the HC anode to 300 mAh/g (ca. 100% SOC, green). The former displays a transmission-line like behavior with a 45° line at high frequencies and a largely capacitive behavior at low frequencies. From the impedance response collected at close to 100% SOC, the HC anode charge transfer resistance (RCT) can be quantified by fitting the semi-circle in the Nyquist plot with an R/Q element. Figure 1b depicts the RCT-values of the HC anode measured at various state-of-charge levels during sodiation and desodiation, showing continuously decreasing RCT values upon Na intercalation. These findings will be compared to the magnitude and the evolution of the cell resistances for the lithiation of the same HC, and implications on the rate capability originating therefrom will be discussed. References [1] D. Pritzl, J. Landesfeind, S. Solchenbach and H. A. Gasteiger., J. Electrochem. Soc. 165 (10), A2145-A2153, 2018. [2] R. Petibon, C. P. Aiken, N. N. Sinha, J. C. Burns, H. Ye, C. M. VanElzen, G. Jain, S. Trussler, and J. R. Dahn et al., J. Electrochem. Soc. 160 (1), A117-A124, 2013. [3] C. Bommier, W. Luo, W.Y. Gao, A. Greaney, S. Ma, X. Ji, Carbon 76, 165–174, 2014. [4] P. Abraham, S. D. Poppen, A. N. Jansen, J. Liu, and D. W. Dees, Electrochim. Acta. 49, 4763-4775, 2004. [5] S. Solchenbach, D. Pritzl, E. Kong, J. Landesfeind, and H. A. Gasteiger, J. Electrochem. Soc. 163 (10), A2265-A2272, 2016. [6] P. Bai, Y. He, X. Zou, X. Zhao, P. Xiong, Y. Xu, Adv. Energy Mater. 1703217, 2018. Figure 1

"Chemical activation" using Brønsted acids as chemical agents is widely used to generate activated carbons for various sorption applications. Commercially relevant is especially a process using phosphoric acid as activating agent applied to abundant and inexpensive biomass such as wood or coconut shells. In this manuscript, we revisit the porogenesis mechanism based on experiments involving molecular model compounds and oxygen-free polymer precursors, as well as different molten acids as activating agents. Describing acid activation with principles of sol-gel chemistry results in a more general understanding and uncovers a versatile synthetic tool for materials nanochemistry.

Single-walled carbon nanotubes (SWCNT) have been covalently cross-linked via a reductive functionalization pathway, utilizing negatively charged carbon nanotubides (KC4). We have compared the use of difunctional linkers acting as molecular pillars between the nanotubes, namely, p-diiodobenzene, p-diiodobiphenyl, benzene-4,4'-bis(diazonium), and 1,1'-biphenyl-4,4'-bis(diazonium) salts as electrophiles. We have employed statistical Raman spectroscopy (SRS), a forefront characterization tool consisting of thermogravimetric analysis coupled with gas chromatography and mass spectrometry (TG-GC-MS) and aberration-corrected high-resolution transmission electron microscopy imaging series at 80 kV to unambiguously demonstrate the covalent binding of the molecular linkers. The present study shows that the SWCNT functionalization using iodide derivatives leads to the best results in terms of bulk functionalization homogeneity ( Hbulk) and degree of addition. Phenylene linkers yield the highest degree of functionalization, whereas biphenylene units induce a higher surface area with an increase in the thermal stability and an improved electrochemical performance in the oxygen reduction reaction (ORR). This work illustrates the importance of molecular engineering in the design of novel functional materials and provides important insights into the understanding of basic principles of reductive cross-linking of carbon nanotubes.

Iron‐ or cobalt‐coordinated heteroatom doped carbons are promising alternatives for Pt‐based cathode catalysts in polymer‐electrolyte fuel cells. Currently, these catalysts are obtained at high temperatures. The reaction conditions complicate the selective and concentrated formation of metal–nitrogen active sites. Herein a mild procedure is introduced, which is conservative toward the carbon support and leads to active‐site formation at low temperatures in a wet‐chemical metal‐coordination step. Active‐site imprinted nitrogen doped carbons are synthesized via ionothermal carbonization employing Lewis‐acidic Mg2+ salt. The obtained carbons with large tubular porosity and imprinted N4 sites lead to very active catalysts with a half‐wave potential (E1/2) of up to 0.76 V versus RHE in acidic electrolyte after coordination with iron. The catalyst shows 4e− selectivity and exceptional stability with a half‐wave potential shift of only 5 mV after 1000 cycles. The X‐ray absorption fine structure as well as the X‐ray absorption near edge structure profiles of the most active catalyst closely match that of iron(II)phthalocyanine, proving the formation of active and stable FeN4 sites at 80 °C. Metal‐coordination with other transition metals reveals that Zn–Nx sites are inactive, while cobalt gives rise to a strong performance increase even at very low concentrations.

Ni nanoparticles supported on nitrogen-doped carbon (NDC) prepared via salt-melt synthesis with a hierarchical porosity were successfully applied as the catalyst for the degradation of Kraft lignin. It is shown that Ni-NDC is more efficient when compared to Ni nanoparticles deposited on an N-free carbon support, prepared with similar porosity features (Ni-C) and to Ni nanoparticles deposited on a commercial carbon (Ni-Cref). The efficiency of these materials was compared for reactions performed both in batch and flow reactors, highlighting the effect of the reactor setup on the stability of the recovered catalysts.

The dissolution of different platinum-based nanoparticles deposited on a commercial high-surface area carbon (HSAC) support in thin catalyst films is investigated using a highly sensitive electrochemical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The previously reported particle-size-dependent dissolution of Pt is confirmed on selected industrial samples with a mean Pt particle size ranging from 1 to 4.8 nm. This trend is significantly altered when a catalyst is diluted by the addition of HSAC. This indicates that the intrinsic dissolution properties are masked by local oversaturation phenomena, the so-called confinement effect. Furthermore, by replacing the standard HSAC support with a support having an order of magnitude higher specific surface area (a micro- and mesoporous nitrogen-doped high surface area carbon, HSANDC), Pt dissolution is reduced even further. This is due to the so-called non-intrinsic confinement and entrapment effects of the (large amount of) micropores and small mesopores doped with N atoms. The observed more effective Pt re-deposition is presumably induced by local Pt oversaturation and the presence of nitrogen nucleation sites. Overall, our study demonstrates the high importance and beneficial effects of porosity, loading and N doping of the carbon support on the Pt stability in the catalyst layer.

Nanoporous carbon materials are known for their applicability in important areas such as sorption, catalysis and electrochemistry (e.g. fuel cell catalysts, supercapacitor or battery electrodes) It was shown that mesoporous nitrogen doped carbons (NDCs) act as an inexpensive and highly active non-metal catalyst in the oxygen reduction reaction (ORR), with the potential to reach performances of practical need one day.1More importantly nitrogen doped carbons are acting as solid-state ligand and support material for non-noble catalysts using low cost transition metals like iron or cobalt. This class of materials has the potential for a disruptive technology in fuel cells e.g. for automotive applications. A key strategy towards improvement for this aim comprises the generation of carbons with advantageous porosity, which typically means high surface area and mass transport pores. My group is developing a novel nanochemistry strategy that is using inorganic salt melts as unconventional reaction medium for the porogenesis, thereby revisiting classic activation techniques.2 Carbon materials with extra high surface area and pore volumes, four times as high as in commercial activated carbons, are obtained.3 In our most recent work we introduce an in-situ template transformation as a new tool to develop anisotropic tubular porosity towards highly porous NDCs. While we previously observed that residual solid salt can introduce additional macroporosity, we herein purposely in-situ crystallize nanoscopic fibrous salt crystals acting as anisotropic templates for mass transport nanopores.4 The utilization of magnesium chloride in contrast to the more commonly used zinc chloride supports the scalability and shows the more general applicability of the salt templating strategy. The obtained NDCs show very high specific surface areas up to 2780 m2 g 1 and outstanding total pore volumes up to 3.86 cm3 g-1, because of the present unique nanochannel pores. In a next step, we exploit the unique porosity for the development of a mild low temperature formation of non-noble oxygen reduction catalysts with the conservation of the doped carbon chemistry. Very active catalysts with a half wave potential of up to 0.76 V vs. RHE in 0.05 M H2SO4 are obtained after metalation with iron. The catalyst shows four electron selectivity and exceptional stability with only a very low performance degradation of down to ∆E1/2 = 5 mV after 1000 cycles between 0.4-1.0 V at 50 mV s-1 in O2-saturated electrolyte. The Fe K-edge fourier transform EXAFS profile of the most active catalyst is almost completely matching that of the iron(II) phthalocyanine, indicating the possibility to create active and stable FeN4 sites for advanced non-noble oxygen reduction electrocatalysts at chemically non-destructive low temperatures. References: 1. (a) Yang, W.; Fellinger, T.-P.; Antonietti, M., Efficient Metal-Free Oxygen Reduction in Alkaline Medium on High-Surface-Area Mesoporous Nitrogen-Doped Carbons Made from Ionic Liquids and Nucleobases. Journal of the American Chemical Society 2010, 133 (2), 206-209; (b) Jaouen, F.; Proietti, E.; Lefevre, M.; Chenitz, R.; Dodelet, J.-P.; Wu, G.; Chung, H. T.; Johnston, C. M.; Zelenay, P., Recent advances in non-precious metal catalysis for oxygen-reduction reaction in polymer electrolyte fuel cells. Energy & Environmental Science 2011, 4(1), 114-130. 2. (a) Fechler, N.; Fellinger, T.-P.; Antonietti, M., “Salt Templating”: A simple and sustainable pathway towards highly porous functional carbons. Advanced Materials 2012, just accepted; (b) Elumeeva, K.; Fechler, N.; Fellinger, T. P.; Antonietti, M., Metal-free ionic liquid-derived electrocatalyst for high-performance oxygen reduction in acidic and alkaline electrolytes. Mater. Horiz. 2014, 1(6), 588-594. 3. Pampel, J.; Fellinger, T. P., Opening of Bottleneck Pores for the Improvement of Nitrogen Doped Carbon Electrocatalysts. Advanced Energy Materials 2016, 6(8). 4. Pampel, J.; Mehmood, A.; Antonietti, M.; Fellinger, T. P., Ionothermal template transformations for preparation of tubular porous nitrogen doped carbons. Materials Horizons 2017, DOI: 10.1039/C6MH00592F.

Electrochemical reactions in the Li-S batteries are considered as a multistep reaction process with at least 2-3 equilibrium states. Here we report a possibility of having a conversion of Li2S into sulfur without detectible formation of polysulfides. That was confirmed by using a novel material system consisting of carbon coated Li2S particles prepared by carbothermal reduction of Li2SO4. Two independent in operando measurements showed direct oxidation of Li2S into sulfur for this system, with almost negligible formation of polysulfides at potentials above 2.5 V vs. Li/Li+. Our results link the diversity of first charge profiles in the literature to the Li2S oxidation mechanism and show the importance of ionic wiring within the material. Furthermore, we demonstrate that the Li2S oxidation mechanism depends on the relative amount of soluble sulfur in the electrolyte. By controlling the type and the amount of electrolyte within the encapsulating carbon shell, it is thereby possible to control the reaction mechanism of Li2S activation. (C) 2017 Elsevier B.V. All rights reserved.

Direct electrochemical formation of hydrogen peroxide (H2O2) from pure O2 and H2 on cheap metal-free earth abundant catalysts has emerged as the highest atom-efficient and environmentally friendly reaction pathway and is therefore of great interest from an academic and industrial point of view. Very recently, novel metal-free mesoporous nitrogen-doped carbon catalysts have attracted large attention due to the unique reactivity and selectivity for the electrochemical hydrogen peroxide formation [1], [2], [3]. In this work, we provide deeper insights into the electrocatalytic activity, selectivity and durability of novel metal-free mesoporous nitrogen-doped carbon catalyst for the peroxide formation with a particular emphasis on the influence of experimental reaction parameters such as pH value and electrode potential for three different electrolytes. We used two independent approaches for the investigation of electrochemical hydrogen peroxide formation, namely rotating ring-disk electrode (RRDE) technique and photometric UV–VIS technique. Our electrochemical and photometric results clearly revealed a considerable peroxide formation activity as well as high catalyst durability for the metal-free nitrogen-doped carbon catalyst material in both acidic as well as neutral medium at the same electrode potential under ambient temperature and pressure. In addition, the obtained electrochemical reactivity and selectivity indicate that the mechanisms for the electrochemical formation and decomposition of peroxide are strongly dependent on the pH value and electrode potential.

The Cover picture shows a concept of using a carbon aerogel as catalyst in air cathodes for microbial fuel cells. This nitrogen-doped ionothermal carbon aerogel (NDC) has a high surface area, large pore volume, and hierarchical porosity. The NDC shows excellent electrocatalytic performance for oxygen reduction at neutral pH. Microbial fuel cells using NDC air cathodes achieve a high maximum power density, higher than most of the state-of-the-art catalysts used as air cathodes, and allow simultaneous wastewater treatment. More details can be found in the Full Paper by Zhang et al. on page 2788 in Issue 19, 2016 (DOI: 10.1002/cssc.201600590).

The use of lignin as a precursor for the synthesis of materials is nowadays considered very interesting from a sustainability standpoint. Here we illustrate the synthesis of a micro-, meso-, and macroporous nitrogen-doped carbon (NDC) using lignin extracted from beech wood via alkaline hydrothermal treatment and successively functionalized via aromatic nitration. The so obtained material is thus carbonized in the eutectic salt melt KCl/ZnCl2. The final NDC shows an excellent activity as electrocatalyst for the oxygen reduction reaction.