Cobaloximes are promising, earth-abundant catalysts for the light-driven hydrogen evolution reaction (HER). Typically, these cobalt(III) complexes are prepared in situ or employed in their neutral form, for example, [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. Herein, we report an interdisciplinary investigation into complex salts [Co(dmgH) 2 (pyWe describe their strategic syntheses from the commercially available complex [Co(dmgH) 2 (py)Cl] and demonstrate that these double and single complex salts are potent catalysts for the light-driven HER. We also show that scanning electrochemical cell microscopy can be used to deposit arrays of catalysts [Co(dmgH) 2 (py 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 by 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", nanoprinted in a desired pattern on a solid support.

To date most studies focusing on light‐driven water splitting for green energy conversion schemes depend on bulk analyses of the produced hydrogen using, e. g., head‐space gas chromatography. In this contribution, we present the fabrication of Pd‐modified microelectrodes for in situ electrochemical hydrogen measurements using de‐alloyed Au−Ni microelectrodes. Stability studies and pH‐dependent investigations revealed the stability of these microsensors over a period of seven days, and confirmed their applicability in a pH range of 3–10 with a limit of detection (LOD)<1 μmol/L. First in situ proof‐of‐principle electrochemical imaging of hydrogen generated at a microelectrode and operando studies of hydrogen evolution at earth‐abundant cobalt hydrogen evolution catalysts using the developed Pd‐microsensors in combination with scanning electrochemical microscopy (SECM) demonstrated the potential of these microsensors for operando studies in light‐driven heterogeneous catalysis.

Chemical functionalization of molecular 2D materials toward the assembly of hierarchical functional nanostructures is of great importance for nanotechnology including areas like artificial photocatalytic systems, nanobiosensors, or ultrafiltration. To achieve the desired functionality of 2D materials, these need to be characterized down to the nanoscale. However, obtaining the respective chemical information is challenging and generally requires the application of complementary experimental techniques. Here, the synthesis and chemical characterization of hierarchically assembled molecular nanosheets based on ≈1 nm thin, molecular carbon nanomembrane (CNM) and covalently grafted, single‐molecule layer cobalt(III) catalysts for the light‐driven hydrogen evolution reaction (HER) is demonstrated. X‐ray photoelectron spectroscopy (XPS) and tip‐enhanced Raman spectroscopy (TERS) to access both the transversal and longitudinal chemical information of the synthesized nanosheets with nanometer resolution are employed. TERS and XPS data provide detailed information on the average and local surface distribution of the catalyst as well as mechanistic details of the grafting reaction. The proposed approach represents a general route toward a nanoscale structural analysis for a variety of molecular 2D materials—a rapidly growing materials class with broad prospects for fundamental science and applications.

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Single and multi-barrel nanopipettes and nanopipette-based scanning electrochemical probe microscopy techniques like scanning electrochemical cell microscopy (SECCM) have gained significant attention as tools for localized, maskless, three-dimensional surface modifications [1,2]. The nanometer-sized orifices of nanopipettes allow delivering molecules to solution inducing concentration-confined electrodepositions. Also, electroless nanoscale depositions like the fountain pen technique [3] can be achieved by this technique. In this study, we present the deposition of various cobaloxime-based earth-abundant Co catalysts for light-driven hydrogen evolution reaction (HER) [4]. Arrays of different cobalt(III) complexes were deposited via SECCM and investigated in respect with their HER activity using scanning electrochemical microscopy (SECM) in combination of Pd-microsensors [5] for in situ hydrogen (H2) measurements under illumination. In addition, AFM studies revealed possible degradation of the commercially available neutral benchmark complex [Co(dmgH)2(py)Cl] in these studies. First results will also be presented in respect with the deposition of nanowires via co-deposition of HER catalyst and Ruthenium photosensitizer. First spatially resolved photocatalytic studies at such nanowires, which are characterized by high surface area, will be presented. Also, the influence of the substrate will also be discussed. References: Oswald, K. Palanisamy, C. Kranz, Curr. Op. Electrochem. 34, 100965 (2022). Hengsteler et al., Nano Lett. 21, 9093 (2021). -H. Kim, N. Moldovan, H.D. Espinosa, Small 1, 632, (2005). Oswald et al., Chem. Eur. J. 27, 16896 (2021) and corrigendum (2022); doi:10.1002/chem.2022008809. Kund et al., ChemElectroChem 9, e202200071 (2022) Funding by the German Science Foundation (DFG) – project number 364549901 – TRR 234 (projects B7, C4).