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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.

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

Functional particles such as TiO2 and Pt/C are often fixed on a flat substrate for practical uses. rotating ring disk electrode (RRDE) technique, in which Pt/C nanoparticles were dispersed on a glassy-carbon (GC) disk electrode, is known as a method capable of evaluating a catalyst activity. The technique was often applied to the evaluation of oxygen reduction catalysts used in fuel cells or metal-air batteries, because the reaction intermediates such as hydrogen peroxide can be detected by the ring electrode. However, the accuracy of the technique was significantly affected by the dispersivity of the catalyst particles on the electrode. Thus, the catalysts on the disk electrode are required to be uniformly dispersed and many researchers have sought the best dispersion method. Although microscope photographic images were used for the estimation of dispersivity on the electrode, no quantitative analyses were performed by using the images. In this study, we have developed a program called “Roughness Analyzer” which can quantitatively analyze the dispersiveness of particles on a flat substrate. This software can load a three dimensional data of particles fixed on a substrate measured by a surface roughness meter (SV-C4500 CNC, Mitutoyo) and display a 2D contour map of the loaded data. It should be noted that, the height of each point is expressed by the brightness of each dot. If necessary, a user can change the range of height represented by the brightness and the number of level. This software is equipped with an auxiliary function to estimate only a substrate surface from a three-dimensional data of the particles fixed on a substrate. This function can automatically determine the points of each cross-section of the 2D contour map that is likely to be surface of the substrate itself, and curves connecting these points was obtained by a spline interpolation method. Thus, only particle-derived height data are calculated by subtracting the height of only the substrate surface data from that of experimental raw data. Analytical functions are “Cluster Analysis” and “Distribution Analysis.” The Cluster Analysis can detect each secondary particle agglomerated on the substrate from the height data. Each secondary particle is filled with a different color and the area, the volume, and the average height of each particle are calculated respectively. The Distribution Analysis can divide the substrate surface in any number from the center of the substrate surface in a radial direction and an angular direction. Further, it can automatically calculate the area, the volume and the percentages of area occupancy of particles in each section. For example, the dispersiveness of a modified GC electrode was evaluated by the software. The electrode was prepared as follows: A 2.0 mg of Pt/MWCNTs was suspended in 1 mL of 0.1 wt% Nafion-EtOH by ultrasonication for 10 min. Then, 10 μL of the suspension was cast onto a glassy-carbon disk (6 mm φ, 0.283 cm2) – Pt ring electrode (Nikko Keisoku) and dried for 1 h at 60°C by using an infrared lamp. Fig. 1 shows the percentage of the area occupancy for the secondary particles in each section. Each cumulative bar represents the percentage of area occupancy in the same radial range, thus, it means good dispersivity of the particles when each cumulative bar has similar height, namely, the standard deviation of the heights is small. Moreover, each element in each cumulative bar means the percentage of area occupancy for the particles at a different angular direction in the same radial range. The desirable dispersivity can be achieved when the standard deviation of the height of the bars is small. However, the small standard deviations are not a sufficient condition for good dispersivity. Criteria for dispersivity are the average height of the particles as well as the standard deviations. Figure 1