Selective oxidation of alcohols to their corresponding aldehyde or carboxylic acid is one of the most important classes of organic synthesis reactions. In addition, electrochemical alcohol oxidation is considered a viable anode reaction that can be paired with H 2 evolution or other reductive fuel production reactions in electrochemical and photoelectrochemical cells. NiOOH, a material that has been extensively studied as an oxygen evolution catalyst, is among the most promising electrocatalysts for selective alcohol oxidation. Electrochemical alcohol oxidation by NiOOH has been understood since the 1970s to proceed through a hydrogen atom transfer to NiOOH. In this study, we establish that there is a second, more dominant general alcohol oxidation pathway on NiOOH enabled at more positive potentials. Using a three-step electrochemical procedure we developed, we deconvoluted the currents corresponding to these two pathways for various alcohols and aldehydes. The results show that alcohols and aldehydes have a distinct difference in their respective preferences for the two oxidation pathways. Our three-step electrochemical procedure also allowed us to evaluate the Ni valence involved with the different oxidation pathways to elucidate their mechanistic differences. Using these experimental results coupled with a computational investigation, we propose that the new pathway entails hydride transfer from the substrate to Ni 4+ sites in NiOOH. This study offers an essential foundation to understand various oxidative electrochemical dehydrogenation reactions on oxide and hydroxide-based catalytic electrodes.

The first step of the hydrogen evolution reaction, an important reaction for the storage of renewable energy, is the formation of a surface-adsorbed hydrogen atom through proton discharge to the electrode surface, commonly known as the Volmer reaction. Herein a theoretical description of the Volmer reaction is presented. In this formulation, the electronic states are represented in the framework of empirical valence bond theory, and the solvent interactions are treated using a dielectric continuum model in the linear response regime. The nuclear quantum effects of the transferring proton are incorporated by quantization along the proton coordinate. The ground and excited state electron−proton vibronic free energy surfaces are computed as functions of the proton donor−acceptor distance and a collective solvent coordinate. In the fully adiabatic regime, the current densities and Tafel slopes are computed from the ground state vibronic free energy surface. This theory is applied to the proton-coupled electron transfer reaction involving proton discharge from H 3 O + in aqueous solution to a gold electrode. This theoretical model opens the door for future studies, including examination of the effects of vibronic nonadiabaticity, electronic friction, and solvent dynamics.

Computational MethodsDensity functional theory (DFT) calculations for geometry optimizations, electronic energy, solvation energy, and vibrational frequencies were performed using the (U)B3LYP hybrid exchange-correlation functional 1 with the D3 dispersion correction, 2 as implemented in the Jaguar software version 7.9. 3 Solvation effects were modeled using the Poisson-Boltzmann continuum (PBF) approximation 4 for acetonitrile (ε = 37.5, r = 2.18).Geometry optimizations were performed in the gas phase (for CO 2 , water, CO, and the TFEH complexes of 2a and 2b) or acetonitrile (all other species, including transition states) using 6-311G**++ basis sets 5 for C, H, N and O, the LACV3P++ basis set and effective core

Analysis of variable-temperature fluorescence quantum yield and lifetime data for per(difluoroboro)tetrakis(pyrophosphito)diplatinate(II) ([Pt(2)(μ-P(2)O(5)(BF(2))(2))(4)](4-), abbreviated Pt(pop-BF(2))), yields a radiative decay rate (k(r) = 1.7 × 10(8) s(-1)) an order of magnitude greater than that of the parent complex, Pt(pop). Its temperature-independent and activated intersystem crossing (ISC) pathways are at least 18 and 142 times slower than those of Pt(pop) [ISC activation energies: 2230 cm(-1) for Pt(pop-BF(2)); 1190 cm(-1) for Pt(pop)]. The slowdown in the temperature-independent ISC channel is attributed to two factors: (1) reduced spin-orbit coupling between the (1)A(2u) state and the mediating triplet(s), owing to increases of LMCT energies relative to the excited singlet; and (2) diminished access to solvent, which for Pt(pop) facilitates dissipation of the excess energy into solvent vibrational modes. The dramatic increase in E(a) is attributed to increased P-O-P framework rigidity, which impedes symmetry-lowering distortions, in particular asymmetric vibrations in the Pt(2)(P-O-P)(4) core that would allow direct (1)A(2u)-(3)A(2u) spin-orbit coupling.