Metal -free hydrogen -bonding conductive polymer catalysts (HCPCs) are emerging alternatives to platinum -group -metals (PGMs) for electrocatalytic hydrogen evolution reaction (HER). In this study, electrodes coated with poly -neutral red (PNR) films were fabricated by oxidative chemical vapor deposition (oCVD) and electropolymerization deposition (EPD) to study their activities as HER-electrocatalysts in acidic media. PNR (EPD) exhibited a superior performance, i.e., an overpotential of 194 mV (at 10 mA cm-2) owing to a high exchange current density of 0.711 mA cm-2. The activity is substantiated by spectroelectrochemical measurements and time -dependent density functional theory (TDDFT) calculation unveiling a doubly reduced and doubly protonated PNRH2 as the reaction intermediate for the evolution of H2. It resulted in a first -order kinetic constant of k = 9.98 x 10-4s-1 to indicate a slow dissociation of PNRH2 to release H2. Large Tafel slope of 176 mV dec-1 also limits the electrocatalytic activity of PNR.

Thin-film organic photovoltaic (OPV) devices represent an attractive alternative to conventional silicon solar cells due to their lightweight, flexibility, and low cost. However, the relatively low optical absorption of the OPV active layers still represents an open issue in view of efficient devices that cannot be addressed by adopting conventional light coupling strategies derived from thick PV absorbers. The light coupling to thin-film solar cells can be boosted by nanostructuring the device interfaces at the subwavelength scale. Here, we demonstrate broadband and omnidirectional photon harvesting in thin-film OPV devices enabled by highly ordered one-dimensional (1D) arrays of nanogrooves. Laser interference lithography, in combination with reactive ion etching (RIE), provides the controlled tailoring of the height and periodicity of the silica grooves, enabling effective tuning of the anti-reflection properties in the active organic layer (PTB7:PCBM). With this strategy, we demonstrate a strong enhancement of the optical absorption, as high as 19% with respect to a flat device, over a broadband visible and near-infrared spectrum. The OPV device supported on these optimized nanogrooved substrates yields a 14% increase in short-circuit current over the corresponding flat device, highlighting the potential of this large-scale light-harvesting strategy in the broader context of thin-film technologies.

Most interface materials for organic solar cells (OSCs) were originally optimized for fullerene-based systems and are now being adapted for non-fullerene acceptor (NFA) based solar cells. This reliance on established interface materials results in a limited choice of interface materials for NFA based OSCs. For vacuum processed organic devices, the concept of doped interface materials is exceptionally successful, but has not yet been translated to modern NFA based devices due to solution processing constraints requiring orthogonal solubility. Herein, we report a novel concept for the development of solution-processed HTL in inverted n-i-p architecture OSCs using doped organic nanoparticles (D-NPs), overcoming solvent compatibility limitations and enabling scalable pro-duction processes. We demonstrate that the functional key interface properties of D-NPs HTLs can be tailored independently over a wide regime. Specifically, conductivity and work function can be optimized separately by varying the dopant concentration and the material system. By using D-NPs as HTL in the n-i-p architecture, power conversion efficiencies (PCE) of over 12 % are achieved for PM6:Y6 based devices. The D-NPs HTL concept is successfully applied to a variety of organic semiconductors used in photovoltaics and opens a new class of tailorable interface materials for solution-processed HTL materials.

Millimeter-long organic fiber arrays of intramolecular charge transfer merocyanine HB194 dye were prepared by evaporation-induced self-assembled method. X-ray diffraction spectroscopy indicated individual fibers are millimeter-sized HB194 single crystals. The elimination of defects and structural disorder enabled photoluminescence microscopy studies that revealed the intramolecular charge transfer (CT), bandgap excitonic state is long-lived and remains largely localized in the absence of pi-orbital stacking in the crystalline structure. These nanosecond lifetimes explain the observation of a photoconductivity response upon irradiation with a 633 nm laser due to dissociation of the delocalized CT exciton to free carriers. At the same time, the photo response was increased 4.5 times by coating of the HB194 fiber array with polyvinyl alcohol. This increase is attributed to the larger dielectric field around the fibers that further facilitates the band-gap (CT) exciton dissociation.

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.

Electrocatalytic hydrogen evolution reaction (HER) is a key process for conversion of renewable electricity to storable hydrogen and is crucial to achieve sustainable energy system. HER currently needs nanoparticles of precious metals as electrocatalysts. Development of alternative catalysts based on abundant materials is therefore necessary. Recently, certain conductive polymers exhibited a high catalytic activity towards HER, as they possess hydrogen bonding sites for stabilization of reaction intermediates [1,2]. Neutral red (NR) is a phenazine dye that has a hydrogen-bonding amino group and can be polymerized as it is an analogue of aniline. We have studied synthesis of poly neutral red (PNR) by oxidative chemical vapor deposition (oCVD) and electropolyerization deposition (EPD) to evaluate their HER electrocatalysis. F-doped Tin Oxide (FTO, Asahi Glass) and Carbon felt (CF, SIGRATHERM® GFA5) were used as substrates. 3 zone tubular furnace was employed for oCVD in which NR vapor was oxidized by sulfuric acid at 325°C under N2 stream. EPD was performed by potential cycling between -0.2 and 1.2 V (vs. Ag/AgCl) for 50 times in a 5 mM NR - 0.1 M H2SO4 aqueous solution under N2. Polyaniline (PANI) was also obtained by EPD for comparison. The samples were characterized by infrared spectroscopy (IR), and UV-visible spectroscopy (UV/Vis). The HER catalysis was evaluated by linear sweep voltammetry (LSV) in a 1 M trifluoromethanesulfonic acid (TfOH) under N2. Although both PANI and PNR were nicely obtained by EPD, the CVs during the film growth significantly differed (Fig. 1). An irreversible anodic peak marked as IV is initially seen for oxidation of aniline to trigger its polymerization to PANI. Then, multiple redox peaks marked as I, II, III continue to grow during the CV scans, which are caused by proton-coupled reversible redox of PANI. On the other hand, an irreversible anodic peak II and reversible couple I are seen for NR. While oxidation of NR results in formation of PNR associated with slight decrease of the magnitude of II, the couple I should be proton-coupled reversible reduction of NR, which gradually become irreversible. It already is a sign of catalytic HER by PNR. It is important to note that no redox peaks of PNR are seen as those of PANI. Fig.1. CVs during EPD of (a) PANI and (b) PNR at 50 mV/s in a 5 mM monomer – 0.1 M H2SO4 on FTO for 50 cycles (Red initial to Blue final). Although significantly broadened, the absorption spectrum of PNR-EPD preserves the character of that of NR monomer, to make it appear dark red (Fig. 2a). On the other hand, PNR-oCVD was black with a featureless spectrum. The FTIR of PNR-EPD also show peaks from the C=C and C=N stretching of the ring system, which are almost in the same positions as those for NR, whereas they are greatly shifted towards shorter wavenumbers for PNR-oCVD, suggesting complete change of the chemical structure during oCVD (Fig. 2b). Both PNR samples, however, show additional peaks assignable to HSO4- or SO42- introduced as dopant to make them conductive. Fig.2. Spectroscopic characterizations: (a) Normalized UV-vis absorption spectra and (b) FTIR spectra of NR, PNR-oCVD, PNR-EPD and PANI. (●: C=C or C=N stretching, ■: δs CH3, ▲: HSO4- / SO42- stretching) The catalytic activity was in the order of PNR-EPD, PNR-oCVD and PANI with the HER overpotential (η for 10 mA cm-2) of 268, 379 and 590 mV, respectively (Fig. 3a). The best performing PNR-EPD also resulted in the largest exchange current density (i0) and the smallest slope of 0.321 mA cm-2 and 174.2 mV dec-1, respectively, from the Tafel plot (Fig. 3b), which are among the top reported for conductive polymer catalysts [1,2]. The poor HER catalytic activity of PANI is to be mentioned, since high conductivity and proton exchanging capabilities are expected for PANI. Stable reversible redox of PANI as seen in Fig. 1 is an indication of stabilization and localization of additional charge by protonation, which is not irreversibly transferred to proton to yield H2. On the other hand, the extra charge cannot be stabilized in the structure of PNR but rather is transferred to achieve HER. In order for the polymers to be catalytically active, we need to seek for polymers which are conductive as well as hydrogen-bonding, but not redox active. Fig.3. HER catalytic activity evaluation: (a) Liner sweep voltammogram (10 mV s−1) and (b) Tafel plot of PNR-EPD and PNR-oCVD as compared to PANI, CF (blank control) in 1 M TfOH electrolyte.

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.

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.

1. Introduction Hydrogen is a promising energy carrier, but is currently produced by steam reforming of fossil fuels to discharge CO2. Water splitting by electricity from renewable resources is an ideal solution. However, expensive and rare metals such as Pt and Ru are needed as electrocatalysts for their high activity and durability. We have recently found that metal-free organic conductive polymer made by polymerization of guanine (PG) exhibits a high catalytic activity for hydrogen evolution reaction (HER) close to that of Pt.1,2,3 Hydrogen bonding sites in PG are supposed to stabilize the reaction intermediates. It is also interesting that a nucleic acid as one of the key components of DNA has such properties for HER catalysis. In this work, we have explored other nucleic acids, namely, adenine, cytosine and thymine for their capabilities of polymerization by oxidative chemical vapor deposition (oCVD) and HER activities. 2. Experimental oCVD was carried out in a 3-zone heating quartz tubular furnace, in which 0.5 g of monomer (set to 300~360°C depending on melting points), oxidant (mixture of 0.5 mL sulfuric acid and 0.5 g sodium sulfate, 360°C) and carbon felt (CF) substrate (1.5 cm × 2.5 cm, Jing Long Te Tan, 360°C) were put under N2 stream (3 L/min). The deposition was maintained for 30 minutes after the set temperatures were reached and then allowed to cool down. FT-IR spectra were measured to check formation of conductive polymers. Linear sweep voltammetry (LSV) was performed at 10 mV/s on the polymer coated CF electrodes in a 0.1 M sulfuric acid under N2 to evaluate overvoltage for hydrogen evolution reaction (HER) at 10 mA/cm2. 3. Results and Discussion A black layer was formed by oCVD of adenine. Its FT-IR spectrum exhibited broad peaks around 3000 cm-1, indicative of hydrogen bonds, as well as several strong peaks below 1000 cm-1, which shows presence of free charge carriers to evoke infrared-activated vibration (IRAV). Since similar features were observed in the FT-IR of PG,2 formation of conductive poly-adenine (PA) is reasonably expected. While oCVD of cytosine also yielded similar black film, suggesting formation of PC, that of thymine did not afford any product on the substrate, despite several trials to change temperatures and other deposition conditions. The difference can be reasoned as adenine and cytosine bear cross-linkable amino groups, whereas thymine does not have one. Preliminary electrochemical study revealed an overvoltage of CA. 700mV, far larger than that of PG (290 mV).2 While PG has a hydrogen donating -NH group and a hydrogen accepting ketone group in α-position, PA does have an -NH group but not a ketone. Such difference in the structure of hydrogen bonding site is a possible reason for the large difference of the catalytic activity. Further studies about the HER electrocatalysis are under investigation. References: Coskun et al., Sci. Adv. 2017, 3, e1700686. Coskun et al., Adv. Mater. interfaces, 2019, 1901364. Coskun et al., Adv. Mater. 2020, 1902177.

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.

Photoswitchable organic field-effect transistors (OFETs) with embedded photochromic materials are considered as a promising platform for development of organic optical memory devices. Unfortunately, the operational mechanism of these devices and guidelines for selection of light-sensitive materials are still poorly explored. In the present work, a series of photochromic dihetarylethenes with a cyclopentenone bridge moiety were investigated as a dielectric/semiconductor interlayer in the structure of photoswitchable OFETs. It was shown that the electrical performance and stability of the devices can be tuned by variation of the substituents in the structure of the photochromic material. In particular, it was found that dihetarylethenes with donor substituents demonstrated the best light-induced switching effects (wider memory windows and higher switching coefficients) in the devices. The operation mechanism of the light-triggered memory devices was proposed based on the differential in situ Fourier transform infrared (FTIR) spectroscopy data and regression analysis of the threshold voltage-programming time experimental dependencies. The established relationships will facilitate further rational design of new photochromic materials, thus paving a way to fast and durable organic optical memories and memory transistors (memristors).

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.

Electrocatalytic hydrogen evolution reaction (HER) is promising to achieve conversion of renewable electricity into storable chemical energy. For practical installation of such technology, it is important to develop active and stable electrocatalysts without relying on rare metal elements. Recently, some metal-free conductive organic polymers such as poly-dopamine (PDA) and poly-guanine (PG) have been found to exhibit stably high catalytic activity towards HER 1-3 . Also, we have achieved polymerization of neutral red (NR) dye, which is chemically analogous to aniline and bears amino groups at a high density. Oxidative chemical vapor deposition (oCVD) or electrodepolymerization deposition (EPD) were the techniques to achieve formation of PNR. PNR exhibited a good catalytic activity for CO 2 reduction reaction (CO 2 RR), although the one prepared by oCVD was about twice as active as that by EPD. Structural disordering of the oCVD sample was supposed to contribute to the catalysis. It is likely that there is an optimum for the balance between conductivity and the density of hydrogen bonding sites. In this study, we have studied electrochemical co-polymerization of NR and aniline to find the optimum design of the catalyst. Electro-polymerization of poly-aniline (PANI), PNR or co-polymer PANI-PNR was carried out at an F-doped tin oxide (FTO) coated conductive glass (Asahi-DU) or a carbon felt (CF, Jing Long Te Tan) substrate by potential cycling between -0.2 and +1.0V vs. Ag/AgCl in aqueous solutions containing ANI, NR or their mixtures at appropriate ratios at a total monomer concentration of 50 mM and 0.1 M H 2 SO 4 for 50 (FTO) or 20 cycles (CF) under N 2 . Linear sweep voltammetry (LSV) was performed on polymer coated CF electrodes in a 0.5 M H 2 SO 4 under N 2 for evaluation of HER catalysis. PANI appeared dark green, PNR red, whereas PANI-PNR was black. These color differences already speak for successful loading of NR into PANI to achieve PANI-PNR copolymer. Cyclic voltammograms (CVs) during EPD of PANI and PNR show the characteristic redox peaks 3 (Fig. 1 a, b). While redox peaks of PANI continue to grow, the reversible redox peaks of NR almost stay the same, since formation of cation radical of NR under the present acidic condition is inefficient. 3 When ANI and NR are blended, however, CV that differ from those for homopolymers of PANI and PNR is obtained (Fig. 1c). Although this CV is not the exact superimpose of the two for PANI and PNR, it suggests the presence of NR in the film and its contribution to the redox behavior. HER current in LSV almost remains the same when CF is coated with PANI, indicating its disability of electrocatalysis (Fig. 1d). Although PANI should be the most conductive among the polymers we tested here, PANI does not possess hydrogen bonding amino groups. PNR only showed moderate catalysis partly due to the small film thickness we could achieve under the current preparation condition. The PANI-PNR copolymer indeed exhibited very high catalytic activity to reduce the overvoltage as small as 250 mV. It is likely that NR provides hydrogen bonding catalytic centers while PANI assures a high conductivity. Thus, a superior catalysis has been achieved by the co-polymer strategy than using the homopolymers. The optimal compositional balance between PANI and PNR should be found by further experimental elaboration. References: Coskun et al ., Mater. , 2020, 1902177. Coskun et al ., Mater. interfaces , 2019, 1901364. Xin Huang et al ., 237th ECS meeting abstract , 2019, 135704. Figure 1

We have established electrochemical self-assembly (ESA) of inorganic / organic hybrid thin films in which the inorganic is CuSCN, known as a wide bandgap p-type semiconductor, whereas the organic is 4-N,N-dimethylamino-4’-N’-methylstilbazolium chromophore (abbreviated as DAS+) as its salt with tosylate (DAST) known to exhibit second-order nonlinear optical property for terahertz emitters. The CuSCN/DAS hybrid thin films by ESA show concerted photoluminescence based on energy transfer from inorganic CuSCN to organic DAS, making us anticipate its potential use in optoelectronic devices [1]. Understanding the mechanism of ESA to obtain tuning knob to maximize its functionality is therefore important. In our previous study, switching of dye loading mechanism has been suggested, depending on DAS concentration (C DAS) in the bath [2]. With low C DAS, the loading is limited by diffusion so that DAS is entrapped within CuSCN crystal grains, while surface reaction of hybridization begins to limit the dye loading with high C DAS, resulting in formation of unique nanostructures as well as phase separation of inorganic and organic domains. The border for the switching of dye loading mechanism was found as the ratio between bulk concentrations of dye and the [Cu(SCN)]+ complex, C DAS/C comp = ca. 1/31 in case of DAS+ [3]. In this study, electrochemical analysis has been performed employing rotating disk electrode (RDE) under variation of bulk concentration of dye (DAST and CNST = 4-cyano-4’-(N’-methyl)stilbazolium tosylate for comparison) to verify the proposed mechanism. CNS+ has a strongly electron withdrawing -CN group and therefore bears a much larger dipole moment of 23.5016 Debye than that of DAS+ (10.1442 Debye) as determined by DFT calculation. Thus, a much stronger interaction of CNS+ with CuSCN (essentially with SCN- ion) is expected than DAS+. The overall behavior of CNS+ has been found exactly the same as DAS+ such as changing the crystal orientation of β-CuSCN to lay down its c-axis and phase transition from β- to α-CuSCN. However, such transitions were found for smaller concentrations of CNS+ than DAS+ because of its stronger affinity with CuSCN. The switching dye loading mechanism and associated change of the hybrid structure has also been observed for CNS. Fig. 1 shows plots of amount of dye loaded into the hybrid thin films against the dye concentrations in the electrolytic bath for DAS+ and CNS+. The steep slopes in low dye concentration range represent diffusion limited loading, whereas the moderate slopes are those limited by surface reaction. The bending points, C DAS = 60 μmol dm-3 and C CNS = 200 μmol dm-3, indicate the switching borders for C comp = 2.5 mM. Because of the increased stability of adsorption of CNS+ on CuSCN surface, diffusion limited loading, thus all dyes reaching the electrode surface buried inside the film, continues to operate up to this high dye concentration. The increased stability of CuSCN/CNS surface complex also resulted in about 3 times more efficient dye uptake in the surface reaction limited regime. These results nicely confirm the validity of the proposed mechanism both for DAS+ and CNS+, and that the switching border can be varied by the stability of CuSCN/dye complex. Full analysis should be able to determine C CNS/C comp ratio as the switching border. [1] K. Uda et al. ACS Omega, 4, 4056-4062 (2019). [2] Y. Tsuda et al., Monatshefte für Chemie, 148, 845-854 (2017). [3] Y. Tsuda et al., J. Electrochem. Soc. 166(9) B3096-B3102 (2019). Figure 1

Among various metal oxides previously tested, Co3O4 is known to be one of the best catalysts for oxygen evolution reaction (OER). In this study, doping of Co ions into nanocrystals of zinc oxide (ZnO) has been achieved by microwave (MW) assisted hydrothermal reaction to form catalytic surface sites for OER combined with highly conductive and stable ZnO for flexible catalyst design and potential enhancement of the catalytic activity. MW-assisted hydrothermal reaction has successfully achieved synthesis of Co-doped ZnO nanocrystals at a low reaction temperature of 160ºC and in a short reaction time of 30 min. Partial replacement of 4-coordinated Zn(II) ions of ZnO with Co(II) ions up to about 10at% has been suggested from evaluation of the products by UV-Vis absorption spectra, morphological observations and X-ray diffraction. The higher addition of Co resulted in its phase-separated precipitation as Co(OH)2. While mesoporous electrode processed from ZnO nanocrystals was totally inactive for water oxidation, that of Co-doped ZnO exhibited a good catalytic activity to achieve about 1 mA cm-2 current of OER with an overvoltage of 0.545 V in a neutral aqueous KCl solution, which in fact was far superior to a Co3O4 electrode known to suffer from its limited conductivity. The doped Co ions are only expected to act as reaction centers for charge transfer on the very surface in contact with the electrolyte, while ZnO acts as a highly conductive and chemically stable host matrix to support the catalyst.

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