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Many biomass intermediates are polyols and selectively oxidizing only a primary or secondary alcohol group is beneficial for the valorization of these intermediates. For example, production of 1,3-dihydroxyacetone, a highly valuable oxidation product of glycerol, requires selective secondary alcohol oxidation. However, selective secondary alcohol oxidation is challenging due to its steric disadvantage. This study demonstrates that NiOOH, which oxidizes alcohols via two dehydrogenation mechanisms, hydrogen atom transfer and hydride transfer, can convert glycerol to 1,3-dihydroxyacetone with high selectivity when the conditions are controlled to promote hydrogen atom transfer, favoring secondary alcohol oxidation. This rational production of 1,3-dihydroxyacetone achieved by selectively enabling one desired dehydrogenation pathway, without requiring alteration of catalyst composition, demonstrates how comprehensive mechanistic understanding can enable predictive control over selectivity.

Hydrogenation and hydrogenolysis are two important reactions for electrochemical reductive valorization of biomass-derived oxygenates such as 5-hydroxymethylfurfural (HMF). In general, hydrogenolysis (which combines hydrogenation and deoxygenation) is more challenging than hydrogenation (which does not involve the cleavage of carbon-oxygen bonds). Thus, identifying factors and conditions that can promote hydrogenolysis is of great interest for reductive valorization of biomass-derived oxygenates. For the electrochemical reduction of HMF and its derivatives, it is known that aldehyde hydrogenation is not a part of aldehyde hydrogenolysis but rather a competing reaction; however, no atomic-level understanding is currently available to explain their electrochemical mechanistic differences. In this study, combined experimental and computational investigations were performed using Cu electrodes to elucidate the key mechanistic differences between electrochemical hydrogenation and hydrogenolysis of HMF. The results revealed that hydrogenation and hydrogenolysis of HMF involve the formation of different surface-adsorbed intermediates via different reduction mechanisms and that lowering the pH promoted the formation of the intermediates required for aldehyde and alcohol hydrogenolysis. This study for the first time explains the origins of the experimentally observed pH-dependent selectivities for hydrogenation and hydrogenolysis and offers a new mechanistic foundation upon which rational strategies to control electrochemical hydrogenation and hydrogenolysis can be developed.

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 H2 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 Ni4+ sites in NiOOH. This study offers an essential foundation to understand various oxidative electrochemical dehydrogenation reactions on oxide and hydroxide-based catalytic electrodes.

A 100% solid, curable liquid encapsulant for photovoltaic modules was developed using acrylic/urethane hybrid chemistry. These liquid acrylics are easily coated and cured with polyisocyanates to form rubbery solids with tunable cure time, excellent optical properties, and UV stability for over 5000 h of accelerated aging. Adhesion to a variety of substrates was good and remained high after aging as well. A variety of catalysts can be used for the curing reaction to tune pot life and cure time. The dielectric strength, surface resistivity, and volume resistivity are similar to commercial encapsulants, and the water vapor transmission rate is lower than EVA. The materials described herein are also useful as optically clear adhesives and potting agents.