• Energy Research

Glyoxal is not likely a key intermediate of CO2 reduction to C2 species, but its electroreduction on Cu yields the commodity chemicals ethylene glycol and ethanol, produced at Cu terraces and defects, respectively.

AbstractPlatinum is a prominent catalyst for a multiplicity of reactions because of its high activity and stability. As Pt nanoparticles are normally used to maximize catalyst utilization and to minimize catalyst loading, it is important to rationalize and predict catalytic activity trends in nanoparticles in simple terms, while being able to compare these trends with those of extended surfaces. The trends in the adsorption energies of small oxygen‐ and hydrogen‐containing adsorbates on Pt nanoparticles of various sizes and on extended surfaces were analyzed through DFT calculations by making use of the generalized coordination numbers of the surface sites. This simple and predictive descriptor links the geometric arrangement of a surface to its adsorption properties. It generates linear adsorption‐energy trends, captures finite‐size effects, and provides more accurate descriptions than d‐band centers and usual coordination numbers. Unlike electronic‐structure descriptors, which require knowledge of the densities of states, it is calculated manually. Finally, it was shown that an approximate equivalence exists between generalized coordination numbers and d‐band centers.

To optimize the performance of catalytic materials, it is paramount to elucidate the dependence of the chemical reactivity on the atomic arrangement of the catalyst surface.

AbstractThe design of active and durable catalysts for the H2O/O2 interconversion is one of the major challenges of electrocatalysis for renewable energy. The oxygen evolution reaction (OER) is catalyzed by SrRuO3 with low potentials (ca. 1.35 VRHE), but the catalyst’s durability is insufficient. Here we show that Na doping enhances both activity and durability in acid media. DFT reveals that whereas SrRuO3 binds reaction intermediates too strongly, Na doping of ~0.125 leads to nearly optimal OER activity. Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO6 octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites.

A fundamental question in the electrochemical CO2 reduction reaction (CO2RR) is how to rationally control the catalytic selectivity. For instance, adding a CO-producing metal like Ag to Cu shifts the latter’s CO2RR selectivity towards C2 products, but the underlying cause of the change is unclear. Herein, we show that CuAg boundaries facilitate the coupling of carbon-containing species to give ethanol, through an otherwise closed pathway. Oxide-derived Cu nanowires mixed with 20 nm Ag particles (Cu:Ag mole ratio of 1:20) reduce CO2 to ethanol with a current density of -4.1 mA/cm2 at -1.1 V vs. RHE and ethanol/ethylene Faradaic efficiency ratio of 1.1. These figures of merit are respectively 5 and 3 times higher than those for pure oxide-derived Cu nanowires. CO2RR using different Ag:Cu ratios and Ag particle sizes reveals that ethanol production scales with CO production on the Ag sites and the abundance of CuAg boundaries, and, very interestingly, without significant modifications to ethylene formation. Computational modelling shows selective ethanol evolution via Langmuir-Hinshelwood *CO + *CHx (x = 1, 2) coupling at CuAg boundaries, and that the formation of energy-intensive CO dimers is circumvented. This work is supported by an academic research fund (R-143-000-683-112) from the Ministry of Education, Singapore and the National University of Singapore Flagship Green Energy Program (R-143-000-A55-646 and R-143-000-A55-733). F.C.-V acknowledges funding from Spanish MICIUN RTI2018-095460–B-I00 and María de Maeztu MDM-2017-0767 grants and, in part, by Generalitat de Catalunya 2017SGR13. O.P. thanks the Spanish MICIUN for a PhD grant (PRE2018-083811). We thank Red Española de Supercomputación (RES) for supercomputing time at SCAYLE (projects QS-2019-3-0018, QS-2019-2-0023 and QCM-2019-1-0034). The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support by NWO. We also thank Cheryldine Lim from the SERIS for assisting with SEM and EDX mapping experiments, and Futian You and Ka Yau Lee from the NUS for assisting with TEM imaging.

Platinum dissolution and restructuring due to surface oxidation are primary degradation mechanisms that limit the lifetime of Pt-based electrocatalysts for electrochemical energy conversion. Here, we studied well-defined Pt(100) and Pt(111) electrode surfaces by in situ high-energy surface X-ray diffraction, on-line inductively coupled plasma mass spectrometry, and density functional theory calculations, to elucidate the atomic-scale mechanisms of these processes. The locations of the extracted Pt atoms after Pt(100) oxidation reveal distinct differences from the Pt(111) case, which explains the different surface stability. The evolution of a specific stripe oxide structure on Pt(100) produces unstable surface atoms which are prone to dissolution and restructuring, leading to one order of magnitude higher dissolution rates We acknowledge the European Synchrotron Radiation Facility for provision of SXRD facilities, and H. Isern and T. Dufrane for their help with the SXRD experiments. Funding is acknowledged from NSERC (grant RGPIN-2017-04045) and Deutsche Forschungsgemeinschaft (grants MA 1618/23 and CH 1763/5-1).

Abstract: Platinum dissolution and restructuring due to surface oxidation are primary degradation mechanisms that limit the lifetime of Pt-based electrocatalysts for electrochemical energy conversion. Here, we studied well-defined Pt(100) and Pt(111) electrode surfaces by in situ high-energy surface X-ray diffraction, on-line inductively coupled plasma mass spectrometry, and density functional theory calculations, to elucidate the atomic-scale mechanisms of these processes. The locations of the extracted Pt atoms after Pt(100) oxidation reveal distinct differences from the Pt(111) case, which explains the different surface stability. The evolution of a specific stripe oxide structure on Pt(100) produces unstable surface atoms which are prone to dissolution and restructuring, leading to one order of magnitude higher dissolution rates. Contents of this repository: 1. SXRD data: The experiments for the acquisition of the raw SXRD data were performed at the the European Synchrotron Radiation Facility, Grenoble, France at the beamlines ID31 and ID03. We thank H. Isern and T. Dufrane for the help during the SXRD experiments. tomo_tomo.spec is the file with the X-ray diffraction metadata for the CTR scans. It is a plain text file. Each HESXRD dataset is saved in a folder, which denotes the potential (e.g. 1V0.zip). The png-image files are previews of the corresponding dataset. The individual raw cbf files can be opened by pyMCA or silx. From python, the images can be accessed using the fabio library. calibration.zip contains the pyFAI calibration files and a list with indexed Bragg reflections for the UB matrix calculation CTRs_parameters.zip contains the averaged CTR structure factors used for the structual analysis as well as files with the atomic coordinates of the refined structural model. steps.zip contains the full datasets from the potential step experiments in Fig. 1e. 2. DFT: CONTCARs.zip contains the atomic coordinates of the optimized computational models.