When it is asked, “where can refractory metals be used?,” the possible shortest answer is, “where cannot they be used?” The uses of refractory‐metal‐based compounds in research and industry are too many to be enumerated; nevertheless, some outstanding examples are briefly mentioned here. Essentially, chalcogenide forms of refractory metals are preferred in the fabrication of high‐performance structures. Therefore, expanding the current studies that usually focus on tungsten‐ and molybdenum‐based structures to other materials may open new opportunities. Moreover, research on ternary and quaternary structures can also be a keystone in creating high‐performance products. The rationale of the present review is to give a brief overview of the recent history of refractory‐metal‐based chalcogenides (RMCs). Initially, the framework is confined to the general design and approaches for the synthesis of refractory metal chalcogenides. The assay is continued by extending with characteristic features of materials from crystalline properties to thermoelectric attributes and examining device fabrication processes. Taken together, the device fabrication part where RMCs are mainly used is extensively focused upon. Finally, outlook and future perspectives are given on the design and construction of RMCs to enable future inspiration and innovation.

Electrochemical hydrogen storage combines the evolution, oxidation, and storage of hydrides from aqueous electrolytes and ionic liquids, but presently requires palladium or rare‐earth metals to achieve significant power capacities. Here hydrogen electrosorption in amine‐activated polydopamine is shown. The organic heterogeneous amine‐hydride yields a gravimetric hydrogen density of 0.44%, corresponding to a 80% hydride‐per‐monomer content, and offers similar reaction kinetics as for palladium and related systems. An initial stability test of 100 electrosorption cycles that demonstrates resilience in acidic media with a tendency for increased capacity over time is included. In situ vibronic amine‐hydride fingerprints corroborate the reversibility and stability of the conversion process and highlight the merits of amine‐activated polydopamines as a heterogeneous organic hydrogen storage system.

Material science is one of the decisive tools toward engineering versatile compounds for numerous technological applications. Over the last decades, thiospinels have been attracting great interest because of their unique characteristics and potential utilizations offering innovative and interesting features. The characteristics of these transition metal sulfides play a key role in many different applications and make thiospinels an essential class of material. To the best of our knowledge, this work, for the first time, summarizes broadband studies on thiospinels reported in the literature. The scope of this review covers all synthesis methods applied over, the chemical and physical properties, and the clean energy applications of thiospinels, which have achieved tremendous significance. It underlined and proposed the challenges and future perspectives based on sulfur-based ternary compounds. Moreover, this review draws attention to the current and future research needs of thiospinel materials to improve and broaden their applications and thus commercialization. (C) 2021 Elsevier Ltd. All rights reserved.

Catalytic processes are contemplated as break point in generating alternative and sustainable energy platforms. The cathodic oxygen reduction reaction (ORR) is an important catalytic system, mainly finding practice in fuel cell and metal-air battery technologies. This work presents the synthesis, structural characterization and electrocatalytic properties of three different Cu2Mo6S8 structures as alternative ORR electrocatalysts. The effect of different carbon additives during synthesis was studied and no positive influence of the carbon addition was indicated. Our findings show that only the bare Cu2Mo6S8 enhances the ORR electro-performance to class with the state-of-the-art ORR catalysts. Excellent stability of 10,000 consecutive ORR cycles, a superior onset potential of 0.894 V and halfwave (E-1/2) potential of 0.641 V vs. reversible hydrogen electrode (RHE) increase the noteworthiness of the Cu2Mo6S8 electrodes. Aside from experimental investigations, density functional theory calculations deliver profound knowledge on the structural and electronic properties (electronic band structure, partial density of states and electron density) of Cu2Mo6S8. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Currently, energy-efficient electrocatalytic oxygen evolution from water involves the use of noble metal oxides. Here, we show that highly p-conducting zinc cobaltite spinel Zn1.2Co1.8O3.5 offers an enhanced electrocatalytic activity for oxygen evolution. We refer to previous studies on sputtered Zn-Co spinels with optimized conductivity for implementation as (p-type) transparent conducting oxides. Based on that, we manufacture off-stoichiometric conducting p-spinel catalytic anodes on tetragonal Ti, Au-Ti and hexagonal Al-doped ZnO carriers and report the evolution of O2 at Tafel slopes between 40.5 and 48 mV dec-1 and at overpotentials between 0.35 and 0.43 V (at 10 mA cm-2). The anodic stability, i.e., 50 h of continuous O2 electrolysis in 1 M KOH, suggests that increasing the conductivity is advantageous for electrolysis, particularly for reducing the ohmic losses and ensuring activity across the entire surface. We conclude by pointing out the merits of improving p-doping in Zn-Co spinels by optimized growth on a tetragonal Ti-carrier and their application as dimension-stable 3d-metal anodes.

The exploration of photocatalytic transformation of solar energy into H-2 through water splitting is an important direction towards sustainable and non-polluting energy in order to cover energy necessity partially. Ternary transition metal chalcogenides have been attracted attention among the other chalcogenides due to their potential applications in the photocatalytic and electrocatalytic hydrogen evolution. Herein, Cu2WS4 nanocubes and Cu2WSe4 nanosheets have been synthesized through a facile hot-injection method to benefit from the advantages such as minimizing the required pressure and reaction time by this technique. The photocatalytic hydrogen evolution activities of Cu2WS4 and Cu2WSe4 have been investigated under the visible light irradiation by using eosin-Y (EY) dye and triethanolamine (TEOA) as a photosensitizer and an electron donor, respectively. Cu2WS4 nanocubes have exhibited higher photocatalytic activity and stability than Cu2WSe4 nanosheets. The photocatalytic HER rates of Cu2WS4 and Cu2WSe4 have been determined as 1260 mu mol g(-1) h(-1) and 861 mu mol g(-1) h(-1), respectively. Photocatalytic HER activities were figured out in the order of Cu2WS4 > Cu2WSe4 which could be attributed to differences between proton reduction potential and the conduction band energy levels. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Electrocatalytic hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR) are the key reactions for conversion of renewable electricity into storable chemical energies. It is crucially important to develop active and stable electrocatalysts without relying on rare metal elements for sustainable energy systems. Recently, some metal-free conductive organic polymers such as polydopamine (PDA) and poly guanine (PGA) synthesized by oxidative chemical vapor deposition (oCVD) have been found to exhibit high catalytic activity and durability for HER and CO2RR1,2. In addition to their conductivity of the π-conjugated system of the main chain, these polymers contain heteroatoms such as N and O at high densities, which are believed to act as hydrogen bonding sites for stabilization of reaction intermediates. However, their exact structures and relationship to the catalytic activities are not fully grasped. In this study, we employ electro-polymerization as the mean to obtain catalytic polymers. Taking polyaniline (PANI) as the host, hydrogen bonding monomers such as dopamine (DA), guanine (GA) and neutral red (NR) are to be introduced to obtain co-polymers with controlled structure and density of the hydrogen bonding sites. Comparison of their electrocatalytic activity to those of the respective homo-polymers should reveal the effective catalytic sites and its product selectivity, which should result in optimal design of the catalyst. Electro-polymerization of PANI and PNR was carried out at an ITO glass substrate in an aqueous solution containing 50 mM ANI or NR and 0.1 M H2SO4 during 50 times potential cycling between -0.5 and +0.6 V vs. Ag/AgCl under the N2. Copolymers were obtained by mixing the monomers at appropriate ratios. The films were characterized by FT-IR spectra. PANI, PNR and their copolymer appeared dark green, dark red and black, respectively. While CVs during electropolymerization of PANI continue to increase the redox peaks of PANI as typically expected, those for PNR show decrease of anodic current suggesting inactiveness of PNR for its redox (Figs. 1 a, b). When they are mixed together, a new redox peak in between those from PANI and another irreversible anodic peak close to +0.9 V appear, which indicate loading of NR in redox active form into PANI (Fig. 1c). The FTIR spectrum of the copolymer showed significant difference from the homo-polymers of PANI and PNR with intense absorption peaks between 800 and 1600 cm-1 (Fig. 1d). These peaks arise from infrared-activated vibrations (IRAV) due to the presence of polaron in the main chain, thus are indicative of its conductive nature. These results suggest improvement of conductivity by heterogeneity in copolymers. Its relevance to the catalytic property and optimal density of hydrogen bonding sites are to be further investigated. References: 1. Coskun et al., Adv. 2017, 3, e1700686. 2. Coskun et al., adv mater interfaces, 2019, 1901364. Figure 1

The most active and efficient catalysts for the electrochemical hydrogen evolution reaction (HER) rely on platinum, a fact that increases the cost of producing hydrogen and thereby limits the widespread adoption of this fuel. Here, a metal-free organic electrocatalyst that mimics the platinum surface by implementing a high work function and incorporating hydrogen-affine hydrogen bonds is introduced. These motifs, inspired from enzymology, are deployed here as selective reaction centres. It is shown that the keto-amine hydrogen-bond motif enhances the rate-determining step in proton reduction to molecular hydrogen. The keto-amine-functionalized polymers reported herein evolve hydrogen at an overpotential of 190 mV. They share certain key properties with platinum: a similar work function and excellent electrochemical stability and chemical robustness. These properties allow the demonstration of one week of continuous HER operation without notable degradation nor delamination from the carrier electrode. Scaled continuous-flow electrolysis is reported and 1 L net molecular hydrogen is produced within less than 9 h using 2.3 mg of polymer electrocatalyst.

The most active and efficient catalysts for the electrochemical hydrogen evolution reaction rely on noble metals, a fact that increases the cost of producing hydrogen and thereby limits the widespread adoption of this fuel. Here we present metal-free polydopamine and polyguanine as selective organic hydrogen electrocatalysts1–3. The conducting functional polymers incorporate selective hydrogen-affine hydrogen bonds that possess a similar hydrogen binding energies and work function as e.g. platinum. We report the synthesis of hydrogen-selective electrocatalytic polyguanine and polydopamine and demonstrate the enhancement of the rate-determining step in the proton reduction. We further present mechanistic spectral IR-operando studies on the catalytic hydrogen bonded motifs as well as the continuous electrolysis to molecular hydrogen using polyguanine and polydopamine electrodes for several 100 hours without notable degradation. (1) Coskun, H.; Aljabour, A.; Schöfberger, W.; Hinterreiter, A.; Stifter, D.; Sariciftci, N. S.; Stadler, P. Cofunction of Protons as Dopant and Reactant Activate the Electrocatalytic Hydrogen Evolution in Emeraldine‐Polyguanine. Adv. Mater. Interfaces 2019, 1901364 DOI: 10.1002/admi.201901364. (2) Coskun, H.; Aljabour, A.; Uiberlacker, L.; Strobel, M.; Hild, S.; Cobet, C.; Farka, D.; Stadler, P.; Sariciftci, N. S. Chemical Vapor Deposition - Based Synthesis of Conductive Polydopamine Thin-Films. Thin Solid Films 2018, 645 (August 2017), 320–325 DOI: 10.1016/j.tsf.2017.10.063. (3) Coskun, H.; Aljabour, A.; Luna, P. De; Sun, H.; Nishiumi, N.; Yoshida, T.; Koller, G.; Ramsey, M. G.; Greunz, T.; Stifter, D.; Hassel, A. W.; Sariciftci, N. S.; Sargent, E. H.; Stadler, P. Hydrogen-Bonded Polymers Mimic Noble Metal Electrocatalysts. Adv. Mater., submitted.

The main electrocatalysts for the electrochemical hydrogen evolution reaction (HER) rely on platinum due to high efficiencies, low binding energy for hydrogen and high electroactive-site density, however the cost of platinum is a crucial limitation for the production of hydrogen by this rare metal.[1] Here, we establish a metal-free and bio-organic electrocatalyst platform that resembles the platinum surface by incorporating hydrogen-affine hydrogen bonds. We introduce keto-amine functional motifs, which act as selective reaction centres.[2, 3] The keto-amine-functionalized biopolymer shown in this work evolve hydrogen at the lowest overpotential in a non-metallic system. With excellent electrochemical stability and chemical robustness, we are able to present a scale-up continuous-flow electrolysis and produce 1 L net molecular hydrogen within less than 9 hours using 2.3 mg of biopolymer electrocatalyst. [1] Y. Zheng, Y. Jiao, Y. Zhu, L.H. Li, Y. Han, Y. Chen, A. Du, M. Jaroniec, S.Z. Qiao, Hydrogen evolution by a metal-free electrocatalyst, Nature Communications, 5 (2014) 3783. [2] H. Coskun, A. Aljabour, P. De Luna, D. Farka, T. Greunz, D. Stifter, M. Kus, X.L. Zheng, M. Liu, A.W. Hassel, W. Schofberger, E.H. Sargent, N.S. Sariciftci, P. Stadler, Biofunctionalized conductive polymers enable efficient CO2 electroreduction, Science Advances, 3 (2017). [3] H. Coskun, A. Aljabour, L. Uiberlacker, M. Strobel, S. Hild, C. Cobet, D. Farka, P. Stadler, N.S. Sariciftci, Chemical vapor deposition - based synthesis of conductive polydopamine thin-films, Thin Solid Films, 645 (2018) 320-325.

A DNA nucleobase is polymerized by oxidative chemical vapor deposition and applied in electrocatalytic hydrogen evolution reaction. The unique synthesis enables the polymerization and protonation of guanine to emeraldine-polyguanine (ePG), analog to polyaniline with four additional and potentially catalytic-active amino functions enhancing the reactivity. Moreover, protons coserve as dopant and reactant in the catalytic electroreduction of protons to molecular hydrogen. More details can be found in article number 1901364 by Halime Coskun and co-workers.

１． Intention Concentration of carbon dioxide (CO2) in the atmosphere has steadily increased since industrial revolution. Despite the recent significant cost reduction of renewable electricity by solar and wind, their intermittency hinders the total shift to renewable energy. It is urgently needed to develop technologies for fast conversion of electrical energy into storable chemical energy by electrolysis, e.g., by water splitting and CO2 reduction. Stable and high-performance electrocatalysts are essential but must be developed without depending on precious metals for the real use and sustainability of the technology. Recently, we have demonstrated high and stable electrocatalytic properties of conductive organic polymers, such as polydopamine (PDA) and polyguanine (PGA) for hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR)1,2). Hydrogen bonding N and O atoms introduced to these polymers are expected to stabilize the reaction intermediates for their high catalytic activities. In this study, a phenazine dye, neutral red (NR) was employed as the monomer to obtain a metal-free catalyst. NR bears many amino functions to make it electropolymerizable just like poly-aniline (electropolymerization deposition, to be called EPD). Also, oxidative chemical vapor deposition (oCVD) was employed to obtain PNR. Synthesis, characterization and comparison of the catalytic activities of PNR by EPD and oCVD are discussed. ２． Experiment EPD of PNR onto carbon felt (CF) was carried out by cycling potential between -1 and +1 V vs. Ag/AgCl for 100 cycles in an aqueous solution containing 0.2 mmol/L NR and 0.5 mol/L KNO3 (pH 5) at 50 mV/s. oCVD of PNR was performed in a three-zone quartz tube furnace under N2 flow, while setting the temperature for NR, sulfuric acid and CF at 375, 220 and 100ºC, respectively, for 240 min. PNR-modified as well as bare CF electrodes were measured under N2 and CO2 in a 1 M KNO3 (pH 7) for their catalytic activities for HER and CO2RR. ３． Result While bare carbon felt (CF) electrode does not show any catalytic activity towards CO2RR, showing about -3 mA cm-2 current at –1 V vs. Ag/AgCl, supposedly dominated by that for HER, the PNR coated CFs show enhanced current (Fig. 1a). That by EPD gives about -5 and -6 mA under N2 and CO2, respectively, indicating its moderate catalytic activity for HER and CO2RR. PNR prepared by oCVD, on the other hand, gives -6 and -12 mA, to demonstrate its superior activity, especially for CO2RR. Chronoamperogram measured during long term electrolysis for 17 h at the oCVD PNR electrode indicates reasonable stability of the catalysis (Fig 1b). These results already nicely confirm catalytic activity of PNR for its conductivity and hydrogen-bonding ability. H. Coskun et al., Sci. Adv. 3, e1700686 (2017). H. Coskun et al., Adv. Mater. Interf. 10, 1901364 (2019). Figure 1

Electrocatalytic CO2-to-CO conversion represents one pathway to upgrade CO2 to a feedstock for both fuels and chemicals (CO, deployed in ensuing Fischer-Tropsch or bioupgrading). It necessitates selective and energy-efficient electrocatalysts-a requirement met today only using noble metals such as gold and silver. Here, we show that the two-dimensional sulfur planes in semimetallic titanium disulfide (TiS2) provide an earth-abundant alternative. In situ Fourier transform infrared mechanistic studies reveal that CO2 binds to conductive disulfide planes as intermediate monothiocarbonate. The sulfur-CO2 intermediate state steers the reduction kinetics toward mainly CO. Using TiS2 thin films, we reach cathodic energy efficiencies up to 64% at 5 mA cm(2). We conclude with directions for the further synthesis and study of semimetallic disulfides developing CO-selective electrocatalysts.

Concentration of carbon dioxide (CO2) in the atmosphere has steadily increased since industrial revolution. Despite the recent significant cost reduction of renewable electricity by solar and wind, their intermittency hinders the total shift to renewable energy. It is urgently needed to develop technologies for fast conversion of electrical energy into storable chemical energy by electrolysis, e.g., by water splitting and CO2 reduction. Stable and high-performance electrocatalysts are essential but must be developed without depending on precious metals for the real use and sustainability of the technology. Recently, we have demonstrated high and stable electrocatalytic properties of conductive organic polymers, such as polydopamine (PDA) and polyguanine (PGA) for hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR)1,2). Hydrogen bonding N and O atoms introduced to these polymers are expected to stabilize the reaction intermediates for their high catalytic activities. In this study, a phenazine dye, neutral red (NR) was employed as the monomer to obtain a metal-free catalyst. NR bears many amino functions to make it electropolymerizable just like poly-aniline (electropolymerization deposition, to be called EPD). Also, oxidative chemical vapor deposition (oCVD) was employed to obtain PNR. Synthesis, characterization and comparison of the catalytic activities of PNR by EPD and oCVD are discussed. EPD of PNR onto carbon felt (CF) was carried out by cycling potential between -1 and +1 V vs. Ag/AgCl for 100 cycles in an aqueous solution containing 0.2 mmol/L NR and 0.5 mol/L KNO3 (pH 5) at 50 mV/s. oCVD of PNR was performed in a three-zone quartz tube furnace under N2 flow, while setting the temperature for NR, sulfuric acid and CF at 375, 220 and 100ºC, respectively, for 240 min. PNR-modified as well as bare CF electrodes were measured under N2 and CO2 in a 1 M KNO3 (pH 7) for their catalytic activities for HER and CO2RR. While bare carbon felt (CF) electrode does not show any catalytic activity towards CO2RR, showing about -3 mA cm-2 current at –1 V vs. Ag/AgCl, supposedly dominated by that for HER, the PNR coated CFs show enhanced current (Fig. 1a). That by EPD gives about -5 and -6 mA under N2 and CO2, respectively, indicating its moderate catalytic activity for HER and CO2RR. PNR prepared by oCVD, on the other hand, gives -6 and -12 mA, to demonstrate its superior activity, especially for CO2RR. Chronoamperogram measured during long term electrolysis for 17 h at the oCVD PNR electrode indicates reasonable stability of the catalysis (Fig 1b). These results already nicely confirm catalytic activity of PNR for its conductivity and hydrogen-bonding ability. References: 1. H. Coskun et al., Sci. Adv., 2017, 3, e1700686. 2. H. Coskun et al., Adv. Mater. Interf., 2019, 10, 1901364. Figure 1

Functional conductive polymers represent an emerging class of nonmetallic electrocatalysts attractive to substitute scarce and expensive elements used today. Here the synthesis of emeraldine‐polyguanine as structural‐molecular analog to polyaniline is shown and the conducting biopolymer as molecular hydrogen electrocatalyst is applied. The polymerized and protonated nucleobase aids the catalytic electroreduction of protons over a peculiar mechanism, where, over amino‐association, protons coserve as dopant and reactant. In acidic media the electrocatalytic evolution of hydrogen at a Tafel slope of 79 mV dec −1 at 290 mV overpotential (10 mA cm −2 ) is reported. The 140h initial stability test demonstrates that the functionality of polymerized nucleobases can be harnessed for heterogeneous catalysis, i.e., as here demonstrated for the electroconversion of hydrogen.

Robust organic thin-film transistors (OTFTs) with high temperature stability allow device integration with mass production methods like thermoforming and injection molding, and enable operation in extreme environment applications. Herein we elaborate a series of materials to make suitable gate dielectric and active semiconductor layers for high temperature stable OTFTs. We employ an anodized aluminum oxide layer passivated with cross-linked low-density polyethylene (LD-PE) to form a temperature-stable gate capacitor. As the semiconductor, we use quinacridone, an industrial organic colorant pigment produced on a mass scale. Evaporated MoOx/Ag source and drain electrodes complete the devices. Here we evaluate the performance of the OTFTs heating them in air from 100 °C in 25 °C increments up to 225 °C, holding each temperature for a period of 30 minutes. We find large differences in stability between quinacridone and its dimethylated derivative, with the former showing the best performance with only a factor of 2 decline in mobility after heating at 225 °C, and unaffected on/off ratio and threshold voltage. The approach presented here shows how industriallys calable fabrication of thermally robust OTFTs can be rationalized.

Electrochemical conversion of CO2 to alcohols is one of the most challenging methods of conversion and storage of electrical energy in the form of high-energy fuels. The challenge lies in the catalyst design to enable its real-life implementation. Herein, we demonstrate the synthesis and characterization of a cobalt(III) triphenylphosphine corrole complex, which contains three polyethylene glycol residues attached at the meso-phenyl groups. Electron-donation and therefore reduction of the cobalt from cobalt(III) to cobalt(I) is accompanied by removal of the axial ligand, thus resulting in a square-planar cobalt(I) complex. The cobalt(I) as an electron-rich supernucleophilic d8-configurated metal centre, where two electrons occupy and fill up the antibonding dz2 orbital. This orbital possesses high affinity towards electrophiles, allowing for such electronically configurated metals reactions with carbon dioxide. Herein, we report the potential dependent heterogeneous electroreduction of CO2 to ethanol or methanol of an immobilized cobalt A3-corrole catalyst system. In moderately acidic aqueous medium (pH = 6.0), the cobalt corrole modified carbon paper electrode exhibits a Faradaic Efficiency (FE%) of 48 % towards ethanol production.

Topological and thermal disorder complicate the mobility characterization in poly(3,4-ethylenedioxythiophene) systems and presently leaves the exact transport mechanisms not fully understood. Here we show that ac-Hall measured by lock-in amplifier is able to resolve the Hall voltage in semimetallic polymers between room temperature and 32 K. These results are evaluated using an organic random phase model. This accounts for the role of tail states and, particularly, for thermal disorder of molecular semiconductors. We report band mobilities up to 3.7 cm(2) V-1 s(-1) in semimetallic polymers occurring in delocalized bands that originate from significant electron coherence across the polymer chains.

Electrocatalysis can be useful in energy conversion, in particular for the production of synthetic fuels from renewable energy. However, this requires catalytic conductors, which sustain the reaction conditions that foremost occur in aqueous solution. Conducting polymers represent a chemically robust but conductive materials class that could be harnessed for aqueous electrocatalytic processes in order to facilitate the important reactions steps to electrosynthesize fuels. In terms of CO2 reduction this has been demonstrated by using a conducting form of polydopamine.(1–3) This system no than other incorporates a richly functionalized backbone able to attach CO2 and electro-reduce to formate efficiently. We shed light on the relevant electro-activation of the incorporated functional themes in the biopolymer and compare this mechanisms to similarly efficient inorganic catalysts. We find that it is the actual nature of the incorporated theme that significantly influences its final selectivity. Such tunability enables the tailoring of selective and highly active catalytic surfaces from organic-functional matter. The functionalzed organic catalysts rely on different reaction mechanisms than state-of-the-art metal-based systems and possibly can be optimized as future sustainable contenders for metal-based electrocatalysts. H. Coskun et al., Chemical vapor deposition - based synthesis of conductive polydopamine thin-films. Thin Solid Films. 645, 320–325 (2018). X. Zheng et al., Sulfur-Modulated Tin Sites Enable Highly Selective Electrochemical Reduction of CO2 to Formate. Joule (2017), doi:10.1016/j.joule.2017.09.014. H. Coskun et al., Biofunctionalized conductive polymers enable efficient CO2 electroreduction. Sci. Adv. 3, e1700686 (2017).

The electrocatalytic reduction of carbon dioxide (CO2) is an attractive option to efficiently bind electrical energy from renewable resources in artificial carbon fuels and feedstocks. The strategy is considered as crucial part in closing the anthropogenic carbon cycle. In particular, the electrosynthetic production of Cl species such as carbon monoxide (CO) would radiate immense power, since these building blocks offer a versatile chemistry to higher carbon products and fuels. In the present study we report the exploration of the catalytic behavior of semiconducting Co3O4 nanofibers for the conversion of CO2 to CO predominantly with a Faradaic efficiency of 65%. We assist the process by expanding the electrode network with nanofibrous interconnections and hence are able to demonstrate the electrosynthesis of CO without applying any metal supplement. We use polyacrylnitrile (PAN) as template polymer to generate highly crystalline Co3O4 fibers to expand the catalytically active surface to volume ratio. The stability of the nanofibrous electrodes remains for 8 h at a geometric current density of approximately 0.5 mA/cm(2) on a flat surface. The ease of synthesis and the comparatively high Faradaic yield for CO makes Co3O4 nanofibers a potential candidate for future large scale electrode utilization.