Accurately predicting adsorption energies of oxygenated aromatic and organic molecules on metal catalysts in the aqueous phase is challenging despite its relevance to many catalytic reactions such as biomass hydrogenation and hydrodeoxygenation. Here, we report the aqueous-phase adsorption enthalpies and free energies of phenol, benzaldehyde, furfural, benzyl alcohol, and cyclohexanol on polycrystalline Pt and Rh determined via experimental isotherms and density functional theory modeling. The experimental aqueous heats of adsorption for all organics are ∼50 to 250 kJ mol–1 lower than calculated gas-phase heats of adsorption, with a larger decrease for Rh compared with that for Pt. Unlike in gas phase, phenol and other aromatic organics adsorb with similar strength on Pt and Rh in aqueous phase. The similar aqueous adsorption strength of phenol and benzaldehyde on Pt and Rh explains their comparable aqueous-phase hydrogenation activities, which are rate-limited by a Langmuir–Hinshelwood surface reaction. A widely used implicit solvation model largely overpredicts the heats of adsorption for all organics compared with experimental measurements. However, accounting for the enthalpic penalty of displacing multiple water molecules upon organic adsorption using a bond-additivity model gives a much closer agreement between experimental measurements and predicted heats of adsorption. This bond-additivity model explains that the similar adsorption strength of organics on Pt and Rh in aqueous phase is due to the stronger adhesion of water to Rh than that on Pt, which offsets the stronger gas-phase organic adsorption energy on Rh. The data reported herein also provides a valuable resource for benchmarking methods for predicting aqueous-phase adsorption energies of C5/C6 organics on metal surfaces.

Bulk heterojunction organic photovoltaic (OPV) devices are multilayer organic devices that can be fabricated using low-cost and scalable solution processing methods, but current devices exhibit poor mechanical stability and degrade under deformation due to cracking and delamination. Recent approaches to improve mechanical durability involve modifying the side-chain or main-chain structures of conjugated polymers in the active layer, but in general it is difficult to simultaneously optimize electronic properties, morphology, and mechanical stability. Here, we present a general approach to improve the mechanical stability of bulk heterojunction active layers through incorporation of an internal elastic network. Network-stabilized bulk heterojunction OPVs are prepared using reactive small molecular additives that are rapidly cross-linked through thiol−ene coupling after processing the active layer. Thiol−ene reactions catalyzed by a base or initiated through short exposure to UV light produce insoluble, elastic thiol−ene networks in the active layer. We show through a combination of crack onset strain measurements, morphological analysis, and OPV device testing that network-stabilized OPVs with up to 20% thiol−ene network exhibit improved deformability with no loss in PCE, and we implement networkstabilized bulk heterojunction OPVs to produce stretchable photovoltaic devices. This work represents a simple approach for improving the mechanical durability of bulk heterojunction OPVs.

Phenol is an important model compound to understand the thermocatalytic (TCH) and electrocatalytic hydrogenation (ECH) of biomass to biofuels. Although Pt and Rh are among the most studied catalysts for aqueous-phase phenol hydrogenation, the reason why certain facets are active for ECH and TCH is not fully understood. Herein, we identify the active facet of Pt and Rh catalysts for aqueous-phase hydrogenation of phenol and explain the origin of the size-dependent activity trends of Pt and Rh nanoparticles. Phenol adsorption energies extracted on the active sites of Pt and Rh nanoparticles on carbon by fitting kinetic data show that the active sites adsorb phenol weakly. We predict that the turnover frequencies (TOFs) for the hydrogenation of phenol to cyclohexanone on Pt(111) and Rh(111) terraces are higher than those on (221) stepped facets based on density functional theory modeling and mean-field microkinetic simulations. The higher activities of the (111) terraces are due to lower activation energies and weaker phenol adsorption, preventing high coverages of phenol from inhibiting hydrogen adsorption. We measure that the TOF for ECH of phenol increases as the Rh nanoparticle diameter increases from 2 to 10 nm at 298 K and −0.1 V vs the reversible hydrogen electrode, qualitatively matching prior reports for Pt nanoparticles. The increase in experimental TOFs as Pt and Rh nanoparticle diameters increase is due to a larger fraction of terraces on larger particles. These findings clarify the structure sensitivity and active site of Pt and Rh for the hydrogenation of phenol and will inform the catalyst design for the hydrogenation of bio-oils.