Spectroscopic calculations of CH and OH bond dissociation energies for aldehydes, ketones, acids, and alcohols

Dilute Au-Containing Ag Nanosponges as a Highly Active and Durable Electrocatalyst for Oxygen Reduction and Alcohol Oxidation Reactions

Zero-dimensional nanoparticles (NPs) have been demonstrated as the promising class of catalysts for various chemical and electrochemical reactions. However, the emerging Au-Ag NP catalysts suffer from single functionality, limited activity enhancement, and unsatisfactory stability problems. Here, we report a facile kinetically controlled solution method to prepare a new class of Au-Ag nanoporous sponges (NSs) composed of three-dimensional networks without using additional stabilizing agents at room temperature. The unexpected shift of the d-band center in our Au-Ag NSs was observed for the first time in Au-Ag bimetallic systems, which effectively activates the Au-Ag NSs for electrochemical reactions. The robust electronic effect coupled with abundant accessible active sites from the hierarchically porous architecture make the bare Au-Ag NSs a superior multifunctional catalyst for oxygen reduction, ethylene glycol (EG) oxidation, and glucose oxidation reactions compared to the commercial Pt/C electrocatalyst in alkaline medium. The optimized AuAg_3.2 NSs deliver a mass activity of 1.26 A mg_Au^-1 toward oxygen reduction reaction, which is ∼8.2 times as high as that of the Pt/C electrocatalyst, simultaneously showing outstanding stability with negligible activity decay after 10 000 cycles. For the anodic reactions, these AuAg_3.2 NSs show extremely high activity and stability toward both EG and glucose catalytic oxidation reactions with a higher mass activity of 7.58 and 1.48 A mg_Au^-1, about 3- and 18.5-fold enhancement than Pt/C, respectively. This work provides important insights into the structural design, performance optimization, and cost reduction to promote the practical applications of liquid fuel cells.

Gold nanocrystal arrays as electrocatalysts for the oxidation of methanol and ethanol

A general difficulty in the comparison of catalysts regarding their electrochemical activities is the significant dependency on the electrode preparation method. In addition to single-crystal, thin-film, and polycrystalline electrodes, most electrocatalysts contain a physical mixture of catalytically active nanocrystals (NCs), conductive carbon support, and binding agent. This type of preparation makes the agglomeration of NCs to larger entities inevitable and simultaneously decreases the catalytically active surface area. In this work, electocatalysts based on two-dimensional arrays of self-assembled monodisperse Au NCs with a particle size of 8 nm have been fabricated. Their electrocatalytic performance in the electrochemical oxidation reaction of methanol and ethanol was investigated for different pH values. The self-assembly of Au NCs into two-dimensional arrays enables to fabricate electrocatalysts with a high mass activity in alkaline electrolytes for alcohol oxidation reactions.

H2O-involved two-electron pathway for photooxidation of aldehydes on TiO2: an isotope labeling study

Aldehyde pollution has been receiving increasing environmental concern recently. In this study, the photooxidation of aldehydes to carboxylates on the TiO2 surface was studied by an oxygen-isotope-labeling method. The solvent H2O was found to contribute much to the oxygen source of the formed carboxylate, which cannot be explained if the conventional O2-involved free radical chain reaction is the only mechanism for the photocatalytic oxidation of aldehydes. We also observed that, unlike in the TiO2 photocatalytic system, the aldehyde oxidation in homogeneous solutions initiated by single electron oxidant (•)OH and SO4(•-) radicals inserted a small O atom of H2O into the product acids. The detailed experiments, combined with DFT calculation, revealed the existence of a new pathway for the oxidation of aldehyde on TiO2, in which, analogous to oxidation of aldehyde by dehydrogenase, the aldehyde undergoes a hydration first and subsequently is oxidized through a two-electron transfer process. The present study highlights the multielectron characteristic of TiO2 photocatalytic oxidation and can have implications for the oxidation of aldehyde in the environment.

Electrocatalytic oxidation of alcohols on gold in alkaline media: base or gold catalysis?

On the basis of a comparison of the oxidation activity of a series of similar alcohols with varying pK(a) on gold electrodes in alkaline solution, we find that the first deprotonation is base catalyzed, and the second deprotonation is fast but gold catalyzed. The base catalysis follows a Hammett-type correlation with pK(a), and dominates overall reactivity for a series of similar alcohols. The high oxidation activity on gold compared to platinum for some of the alcohols is related to the high resistance of gold toward the formation of poisoning surface oxides. These results indicate that base catalysis is the main driver behind the high oxidation activity of many organic fuels on fuel cell anodes in alkaline media, and not the catalyst interaction with hydroxide.