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A thiolated bis(cobalt) cofacial diporphyrin chemisorbed on an edge plane pyrolytic graphite electrode has the electrocatalytic activity of a four-electron (n g 3.6) dioxygen reduction catalyst. When chemisorbed on a gold electrode surface, the same catalyst exhibits the activity of only a two-electron catalyst, producing hydrogen peroxide (n ) 2.1). The edge plane graphite surface thus plays a crucial, but not understood, role in designed dioxygen reduction catalysis. Analysis of X-ray photoelectron spectroscopy and UV-vis results is consistent with the rings of the thiolated porphyrins being coplanar to the Au electrode plane. A structurally modified catalyst exhibits greater coplanarity and a slight increase in activity (n ≈ 2.4). The present results set the stage for a strategy of cochemisorbing functionalities onto the thiolated diporphyrin-coated Au surface, seeking those functionalities which will chemically mimic the graphite surface and elevate the catalytic reactivity to a four-electron dioxygen reduction. Such functionalities could include host-guest cochemisorption of putative carbon surface ligands within the porphyrin electrode cavity. † Present address: Collman, J. P.; Hutchison, J. E.; Lopez, M. A.; Tabard, A.; Guilard, R.; Seok, W. K.; Ibers, J. A.; L'Her, M. J. Am. Chem. Soc. 1992, 114, 9869-9877.(3) (a) Collman, J. P.; Hendricks, N. H.; Leidner, C. R.; Ngameni, E.; L'Her, M. Inorg. Chem. 1988, 27, 387. (b) Collman, J. P.; Wagenknecht, P. S.; Hutchison, J. E.

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Single‐atom catalysts (SACs) represent a new frontier in heterogeneous catalysis due to their remarkable catalytic properties and maximized atomic utilization. However, single atoms often bond to the support with polarized electron density and thus exhibit a high valence state, limiting their catalytic scopes in many chemical transformations. Here, it is demonstrated that 2D black phosphorus (BP) acts as giant phosphorus (P) ligand to confine a high density of single atoms (e.g., Pd1, Pt1) via atomic layer deposition. Unlike other 2D materials, BP with relatively low electronegativity and buckled structure favors the strong confinement of robust zero‐valent palladium SACs in the vacancy site. Metallic Pd1/BP SAC shows a highly selective semi‐hydrogenation of phenylacetylene toward styrene, distinct from metallic Pd nanoparticles that facilitate the formation of fully hydrogenated products. Density functional theory calculations reveal that Pd atom forms covalent‐like bonding with adjacent P atoms, wherein H atoms tend to adsorb, aiding the dissociative adsorption of H2. Zero‐valent Pd in the confined space favors a larger energy gain for the synthesis of partially hydrogenated product over the fully hydrogenated one. This work provides a new route toward the synthesis of zero‐valent SACs on BP for organic transformations.

Thin films of poly[Ru(vbpy)2(py)2]2+ (vbpy is 4-vinyl-4‘-methyl-2,2‘-bipyridine; py is pyridine) have been deposited on electrodes by reductive electropolymerization. Photolysis of the films in the presence of chloride ion leads to photochemical loss of the pyridine ligands and sequential formation of poly[Ru(vbpy)2(py)Cl]+ and poly[Ru(vbpy)2Cl2], as determined by cyclic voltammetry and FTIR spectroscopy. Contact lithography was used to control the photosubstitution process spatially and form laterally resolved, bicomponent films with image resolution below 10 μm. Small spot X-ray photoelectron spectroscopy (XPS) was used to confirm that the photolyzed and nonphotolyzed regions of an imaged film were chemically distinct. Dramatic changes occur in the absorption spectra and redox potentials of the ruthenium complexes upon substitution of chloride for the pyridine ligands. This provides a basis for the fabrication of bicomponent, electrochromic film assemblies on optically transparent electrodes of tin doped indium oxide on glass. The spectroelectrochemical response of these films has been studied by slow scan cyclic voltammetry and potential step chronoamperometry.