Abstract
Bis(diimino)metal (MDI) nanosheets (M = Ni, Co, Cu) are synthesized within a few minutes on indium tin oxide (ITO), glassy carbon (GC), and carbon paper (CP) by electro-oxidation of an aqueous solution of metal ions, hexaaminobenzene trihydrochloride, and ammonia. Thin films of these materials are firmly immobilized directly on the substrate. Their PXRD patterns are similar to those prepared by chemical oxidation, indicating considerable crystallinity. Electrocatalytic activities of MDIs on GC in hydrogen evolution reaction were investigated using rotating disk voltammetry. NiDI affords the lowest overpotential for HER among known coordination nanosheet (CONASH) catalysts and offers high catalytic robustness.
Highlights
Bis(diimino)metal (MDI) nanosheets (M = Ni, Co, Cu) are synthesized within a few minutes on indium tin oxide (ITO), glassy carbon (GC), and carbon paper (CP) by electro-oxidation of an aqueous solution of metal ions, hexaaminobenzene trihydrochloride, and ammonia
Due to the possibility of implanting πconjugated orbitals into flat systems, 2D catalysts afford much higher electrical conductivity[3−5] than their 3D counterparts, which are essential in electrocatalysis
Various exfoliated 2D transition metal dichalcogenides and chemically modified graphenes have been employed in hydrogen evolution reactions (HERs), and as oxygen evolution reaction and oxygen reduction reaction electrocatalysts.[16]
Summary
MDIs and outperforms other coordination nanosheet catalysts (Table 1). Notably, electrosynthesized NiDI showed a significant improvement of 439 mV overpotential at 10 mA cm[2] over chemically synthesized NiDI. CuDI shows a linear region from 430 to 460 mV with a Tafel slope of 118.9 mV dec−1 These values are close to that for the Volmer−Heyrovsky reaction mechanism. NiDI, CoDI, and CuDI show values of 0.185, 0.048, and 0.001 mA cm−2, respectively These electrochemically synthesized MDI modified electrodes show higher current density than other CONASH modified electrodes. NiDI, CoDI, and CuDI have been successfully synthesized electrochemically and directly immobilized on ITO, GC, and CP. They show moderate crystallinity and unique mixed-valence states. NiDI shows the best performance among them and constitutes a better electrocatalyst than other reported CONASHs. Its durability under electrocatalytic conditions is higher than that of chemically synthesized nanosheets. Supplementary figures and experimental details, including experimental procedures, syntheses, characterization, and electrochemical measurements (PDF)
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