Direct Synthesis of Hydrogen Peroxide Over Au–Pd Catalysts Prepared by Electroless Deposition

Effect of Pd Coordination and Isolation on the Catalytic Reduction of O2 to H2O2 over PdAu Bimetallic Nanoparticles

The direct synthesis of hydrogen peroxide (H₂ + O₂ → H₂O₂) may enable low-cost H₂O₂ production and reduce environmental impacts of chemical oxidations. Here, we synthesize a series of Pd₁Au_x nanoparticles (where 0 ≤ x ≤ 220, ∼10 nm) and show that, in pure water solvent, H₂O₂ selectivity increases with the Au to Pd ratio and approaches 100% for Pd₁Au₂₂₀. Analysis of in situ XAS and ex situ FTIR of adsorbed ¹²CO and ¹³CO show that materials with Au to Pd ratios of ∼40 and greater expose only monomeric Pd species during catalysis and that the average distance between Pd monomers increases with further dilution. Ab initio quantum chemical simulations and experimental rate measurements indicate that both H₂O₂ and H₂O form by reduction of a common OOH* intermediate by proton-electron transfer steps mediated by water molecules over Pd and Pd₁Au_x nanoparticles. Measured apparent activation enthalpies and calculated activation barriers for H₂O₂ and H₂O formation both increase as Pd is diluted by Au, even beyond the complete loss of Pd-Pd coordination. These effects impact H₂O formation more significantly, indicating preferential destabilization of transition states that cleave O-O bonds reflected by increasing H₂O₂ selectivities (19% on Pd; 95% on PdAu₂₂₀) but with only a 3-fold reduction in H₂O₂ formation rates. The data imply that the transition states for H₂O₂ and H₂O formation pathways differ in their coordination to the metal surface, and such differences in site requirements require that we consider second coordination shells during the design of bimetallic catalysts.

A zinc-quinone battery for paired hydrogen peroxide electrosynthesis

Hydrogen peroxide is a commodity chemical with immense applications as an environmentally benign disinfectant for water remediation, a green oxidant for synthetic chemistry and pulp bleaching, an energy carrier molecule and a rocket propellant. It is typically synthesized by indirect batch anthraquinone process, where sequential hydrogenation and oxidation of anthraquinone molecules generates H₂O₂. This highly energy demanding catalytic sequence necessitates the advent of new reaction pathways with lower energy expenditure. Here we demonstrate a Zn-quinone battery for paired H₂O₂ electrosynthesis at the three phase boundary of its cathodic half-cell during electric power generation. The catalytic quinone half-cell of the Zn-quinone battery, mediates proton coupled electron transfer with molecular oxygen during its chemical regeneration thereby pairing peroxide electrosynthesis with electricity generation. Hydrogen peroxide synthesizing Zn-quinone battery (HPSB) demonstrated a peak power density of ~90 mW/cm² at a peak current density of ~145 mA/cm² while synthesizing ~230 mM of H₂O₂. HPSB offers immense opportunities as it distinctly couples electric power generation with peroxide electrosynthesis which in-turn transforms energy conversion in batteries truly multifunctional.

Realistic Surface Descriptions of Heterometallic Interfaces: The Case of TiWC Coated in Noble Metals

Noble metal-coated core-shell nanoparticles have been applied to a suite of catalytic applications, with the aim of decreasing the noble metal loading while ideally improving their performance. The chemistry and therefore activity at the surface of these materials are intimately related to the accurate description of the core-shell interface. Using density functional theory, we developed a procedure to obtain realistic surface topology descriptions at the heterometallic junction. This procedure was applied to a topical series of catalysts: Ti_0.1W_0.9C coated in atomically thin monolayers of noble metals. Our quantum chemical calculations provide access to both relevant surface descriptions of these materials and also rationalize several experimental observations. Our general procedure paves the way for the rationalization and prediction of next-generation heterometallic catalysts.