Sol−gel processing of water‐soluble carbon nitride enables high‐performance photoanodes **

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high‐quality, binder‐free PCN films and electrodes has been a largely elusive goal to date. Here, we tackle this challenge by devising, for the first time, a water‐based sol−gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The sol−gel process capitalizes on the use of a water‐soluble PHI precursor that allows formation of a non‐covalent hydrogel. The hydrogel can be deposited on conductive substrates, resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented photoelectrochemical (PEC) performance in alcohol reforming and highly selective (∼100 %) conversions with very high photocurrents (>0.25 mA cm −2 under 2 sun) down to <0 V vs. RHE. This enables even effective PEC operation under zero‐bias conditions and represents the very first example of a ‘soft matter’‐based PEC system capable of bias‐free photoreforming. The robust binder‐free films derived from sol−gel processing of water‐soluble PCN thus constitute a new paradigm for high‐performance ‘soft matter’ photoelectrocatalytic systems and pave the way for further applications in which high‐quality PCN films are required.Completely unbiased : Robust binder‐free films derived from sol−gel processing of a water‐soluble polymeric carbon nitride precursor exhibit unprecedented performance in photoelectrocatalytic reforming of alcohols, including effective operation under bias‐free conditions

Cobaloxime complex salts : synthesis, patterning on carbon nanomembranes and heterogeneous hydrogen evolution studies

Cobaloximes are promising, earth-abundant catalysts for the light-driven hydrogen evolution reaction. Typically, these cobalt(III) complexes are prepared in situ or employed in their neutral form, e.g. [Co(dmgH 2 )(py)Cl], even though related complex salts have been reported previously and could in principle offer improved catalytic activity as well as more efficient immobilization on solid support. Here we report an interdisciplinary investigation into complex salts [Co(dmgH) 2 (py) 2 ] + [Co(dmgBPh 2 ) 2 Cl 2 ] - , TBA + [Co(dmgBPh 2 ) 2 Cl 2 ] - and [Co(dmgH) 2 (py) 2 ] + BArF - . We describe their strategic syntheses from commercially available complex [Co(dmgH) 2 (py)Cl] and demonstrate that these double and single complex salts are potent catalysts for the light-driven hydrogen evolution reaction. We also show that scanning electrochemical cell microscopy can be used to deposit arrays of catalysts [Co(dmgH) 2 (py) 2 ] + [Co(dmgBPh 2 ) 2 Cl 2 ] - and [Co(dmgH) 2 (py)Cl] on supported and free-standing amino-terminated ~ 1 nm thick carbon nanomembranes (CNMs). Photocatalytic H 2 evolution at such arrays was quantified with Pd microsensors using scanning electrochemical microscopy, thus providing a new approach for catalytic evaluation and opening up novel routes for the creation and analysis of “designer catalyst arrays”, nano-printed in a desired pattern on a solid support

Sol–Gel Processing of Water-Soluble Carbon Nitride Enables High-Performance Photoanodes

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high-quality, binder-free PCN films and electrodes has been a largely elusive goal to date. Here we tackle this challenge by devising, for the first time, a sol–gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The sol–gel process capitalizes on the use of a water-soluble PHI precursor that allows formation of a non-covalent hydrogel. The hydrogel can be deposited on conductive substrates resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented PEC performance in alcohol reforming and selective (~100%) conversions with very high photocurrents down to ~0 V vs. RHE, which enables even effective operation under bias-free conditions. The robust binder-free films derived from sol–gel processing of water-soluble PCN thus represent a new paradigm for high-performance ‘soft-matter’ photoelectrocatalytic systems, and pave the way for further applications in which high-quality PCN films are required

Activation by oxidation and ligand exchange in a molecular manganese vanadium oxide water oxidation catalyst

Despite their technological importance, reaction mechanisms of most water oxidation catalysts (WOCs) are poorly understood. We combine theoretical and experimental methods to reveal mechanistic insights into the reactivity of the highly active molecular WOC [Mn4V4O17(OAc)3]3-. Using density functional theory, electrochemistry and IR-spectroscopy, we propose a three-step activation mechanism: one-electron oxidation [Mn3+2Mn4+2]→[Mn3+Mn4+3], acetate-to-water ligand exchange, and another one-electron oxidation [Mn3+Mn4+3]→[Mn4+4]. Analysis of ligand exchange pathways shows that nucleophilic attack of water molecules along the Jahn-Teller axis of Mn3+ centers leads to lower activation barriers than attack at Mn4+ centers. Deprotonation of one water ligand by the leaving acetate group leads to formation of the activated species [Mn4V4O17(OAc)2(H2O)(OH)]1-. Computed Redox potentials are in excellent agreement with electrochemical measurements. This interplay between redox chemistry and ligand exchange controls the formation of the catalytically active species. These results provide key reactivity information essential to further study bio-inspired molecular WOCs and solid-state manganese oxide catalysts