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A facile synthetic pathway using poly(4-vinylpyridine) as a polypyridyl platform is reported for the formation of a metallopolymer. Electrochemical studies indicate that the metallopolymer acts as an efficient H2 evolution catalyst similar to cobalt polypyridyl complexes. It is also observed that the metallopolymer is transformed to cobalt particles when a cathodic potential is applied in the presence of an acid. Electrochemical measurements indicate that an FTO electrode coated with these cobalt particles also acts as an efficient hydrogen evolution catalyst. Approximately 80 µmoles of H2 gas can be collected during 2 h of electrolysis at − 1.5 V (vs. Fc+/0) in the presence of 60 mM of acetic acid. A comprehensive study of the electrochemical and electrocatalytic behavior of cobalt-poly(4-vinylpyridine) is discussed in detail. Graphical Abstract: Poly(4-vinylpyridine) as a precursor for electrodeposited cobalt particles: a cobalt coat derived by a metallopolymer acts as an efficient H2 evolution catalyst. It can transform to a cobalt coat when a potential above − 1.1 V is applied in acid medium. Exchange current density of 10−2.67 mA cm−2 was observed from the Co-coat at − 1.5 V (vs. Fc+/0). Acknowledgements The authors thank the Science and Technology Council of Turkey, TUBITAK (Project No: 215Z249) for financial support. Emine Ülker thanks TUBITAK for support (Project No: 1929B011500059).

Non-oxide cobalt based water oxidation electrocatalysts have received attention recently for their relative ease in preparation since they are easy to prepare, stable both in acidic & basic media, and they have higher turnover frequencies compared to cobalt oxides. Recent studies show that one of the main bottlenecks in implementing non-oxide systems to water splitting is the low number of active metal sites, which is in the order of nmol.cm−2. Herein a new series of non-oxide water oxidation catalysts have been introduced to the field. Cobalt dicyanamides are observed to have around four times higher surface active sites and better catalytic performances than cyanide based systems. Long term catalytic studies (70 h) at an applied potential of 1.2 V and electrochemical studies performed in solutions in pHs ranging from 3.0 to 12.0 indicate that the compounds are robust and retain their structures even under drastic conditions. Moreover, addition of nickel impurities to cobalt dicyanamides has been introduced as a feasible method to improve their catalytic activities.

The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co3(BO3)2, with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co3(BO3)2@CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm−2 for Co3(BO3)2@CNT compared with 3.9 nmol cm−2 for Co3(BO3)2. Co3(BO3)2@CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm−2, respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions. The authors thank the Science and Technology Council of Turkey, TUBITAK (Project No: 214Z095) for financial support. E.U. thanks TUBITAK for support (Project No: 1929B011500059). Y.D. thanks BAGEP and TÜBA-GEBİP for young investigator awards and ECOSTBio (CM 1305) for support. TUBITAK TRGRID infrastructure is gratefully acknowledged for HPC resources.

Although several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process. The authors thank the Science and Technology Council of Turkey, TUBITAK (Project No. 215Z249) for financial support. E.U. thanks TUBITAK for support (Project No. 1929B011500059). Y.D. acknowledges ECOSTBio (CM 1305) for support and thanks the M.N. Parlar Foundation, BAGEP, and TÜBA-GEBİP for young investigator awards. TUBITAK TRGRID infrastructure is gratefully acknowledged for HPC resources. We also thank Prof. Burak Ülgüt for helpful discussions on electrochemistry.

Research on H2 production has recently been directed to the development of cost-efficient and robust heterogeneous catalysts for hydrogen evolution reaction (HER). Given the promising catalytic activities of several cobalt-based systems and the robustness of Prussian blue analogues in harsh catalytic processes including water oxidation, a Co-Co Prussian blue analogue was investigated as a HER catalyst for the first time. Co-Co Prussian Blue modified fluorine doped tin oxide (FTO) electrode demonstrated a significant HER activity with an onset overpotential of 257 mV, a Tafel slope of 80 mV dec−1, and a turnover frequency of 0.090 s−1 at an overpotential of 250 mV. Comparative XPS, Infrared, and XRD studies performed on pristine and post-catalytic electrodes confirm the stability of the catalyst. Acknowledgements This work was suppoerted by the Grants from The Science and Technology Council of Turkey, TUBITAK (Project No: 215Z249). E. U. thanks TUBITAK for support (Project No: 1929B011500059).

WOS: 000374187700008 PubMed: 26970788 Modified electrode based on combination of different conductive polymers (polyaniline -poly(3-methylthiophene) poly( 3,3'-diaminobenzidine) (PANI - P3MT - PDAB)) was previously synthesized in dichloromethane containing HClO4 and tetrabutylammoniumperchlorate (TBAP) as supporting electrolyte. Herein, the determination of hydroquinone (HQ) with amperometric I-t method over this modified and its homopolymers coated electrode was successfully carried out in river water as a real sample and in solution consisting of NaHSO4/Na2SO4 (pH 2.0). For this method, potentials between 0.45 V and 0.65 V were applied and the best analytical response was obtained at 0.55 V using this modified electrode when compared to its homopolymers. the limit of detection (LOD), limit of quantification (LOQ), the linear dynamic range and regression coefficient (R-2) were found as 1.31 x 10(-4) mM, 4.37 x 10(-4) mM, 4.37 x 10(-4)-95.0 mM and 0.998, respectively. These results were compared to homopolymers coated and uncoated Pt electrodes. For checking on the accuracy of the developed method and the matrices interference, determination of HQ was performed in artificially contaminated river water samples with HQ concentration of 5.0 mM and 10.0 mM using this modified electrode and recovery values were calculated as 100.6% and 100.1%, respectively. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [111T445]; Recep Tayyip Erdogan University, Unit of Scientific ResearchRecep Tayyip Erdogan University [2013.102.02.3] This research was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) (Project no: 111T445) and Recep Tayyip Erdogan University, Unit of Scientific Research (Project no: 2013.102.02.3). We thank to Dr. Selcuk Demir (Recep Tayyip Erdogan University, Faculty of Science & Arts, Department of Chemistry, Rize) for improving the language of this munucript.