Press notice. EC agricultural price indices. Trends in EC agricultural price indices (output and input): 1st quarter 1985. 1985.3

The high precious metal loading and high overpotential of the oxygen evolution reaction (OER) prevents the widespread utilization of polymer electrolyte membrane (PEM) water electrolyzers. Herein we explore the OER activity and stability in acidic electrolyte of a combined IrO_<i>x</i>/RuO₂ system consisting of RuO₂ thin films with submonolayer (1, 2, and 4 Å) amounts of IrO_<i>x</i> deposited on top. Operando extended X-ray absorption fine structure (EXAFS) on the Ir L-3 edge revealed a rutile type IrO₂ structure with some Ir sites occupied by Ru, IrO_<i>x</i> being at the surface of the RuO₂ thin film. We monitor corrosion on IrO_<i>x</i>/RuO₂ thin films by combining electrochemical quartz crystal microbalance (EQCM) with inductively coupled mass spectrometry (ICP-MS). We elucidate the importance of submonolayer surface IrO_<i>x</i> in minimizing Ru dissolution. Our work shows that we can tune the surface properties of active OER catalysts, such as RuO₂, aiming to achieve higher electrocatalytic stability in PEM electrolyzers

Real-Time Detection of Acetaldehyde in Electrochemical CO Reduction on Cu Single Crystals

Copper is known to be versatile in producing various products from electrochemical CO2 reduction reaction (eCO2RR), and the product preference depends on reaction environments. The literature has reported that alkaline electrolytes favor acetate production and proposed hypotheses on reaction pathways accordingly. However, our work shows acetate can also come from the fast non-Faradaic chemical oxidation of acetaldehyde in alkaline environments. This adds uncertainties into measurements of both acetaldehyde and acetate production and leads to untrustful investigations on the reaction mechanism as a consequence. With an electrochemistry-mass spectrometry combined (EC-MS) system, we not only demonstrate why and how the imprecise acetaldehyde and acetate production occurs in previous research but also present immediate detection of acetaldehyde as a function of applied potential on single crystal Cu electrodes during electrochemical CO reduction reaction (eCORR). Moreover, the quantified acetaldehyde-to-ethylene production rate ratio provides insightful information on the acetaldehyde-to-ethylene bifurcation point in eCO2RR and thus helps understand the reaction pathways

Selective CO Methanation on Highly Active Ru/TiO₂ Catalysts: Identifying the Physical Origin of the Observed Activation/Deactivation and Loss in Selectivity

Ru/TiO₂ catalysts are highly active and selective in the selective methanation of CO in the presence of large amounts of CO₂ but suffer from a considerable deactivation and loss of selectivity during time on stream. Aiming at a fundamental understanding of these processes, we have systematically investigated the physical reasons responsible for these effects, using catalysts with different surface areas and combining time-resolved kinetic and <i>in situ</i>/<i>operando</i> spectroscopy measurements as well as <i>ex situ</i> catalyst characterization. This allowed us to identify and disentangle contributions from different effects such as structural effects, adlayer effects, such as site blocking effects, and changes in the chemical (surface) composition of the catalysts. <i>Operando</i> X-ray absorption near edge spectroscopy (XANES)/extended X-ray absorption fine structure analysis (EXAFS) measurements revealed that an initial activation phase is largely due to the reduction of oxidized Ru species, together with a distinct change in the Ru particle shape, until reaching a state dominated by metallic Ru species (fraction RuO₂ < 5%) with the highest Ru mass normalized activity. The losses of activity and selectivity during the subsequent deactivation phase are mainly due to slow Ru particle growth (EXAFS, transmission electron microscopy (TEM)). Surface blocking by adsorbed species such as surface formate/carbonate or surface carbon species, which are formed during the reaction, contributes little, as concluded from <i>in situ</i> infrared (IR), temperature-programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS) data. Consequences on the selectivity for CO methanation, which decreases with time on stream for catalysts with larger surface area and for the distinct loss of adsorbed CO and surface formate species, as well as the role of the catalyst surface area in the reaction are discussed

Tuning Surface Reactivity and Electric Field Strength via Intermetallic Alloying

Many electrosynthesis reactions, such as CO2 reduction to multicarbon products, involve the formation of dipolar and polarizable transition states during the rate-determining step. Systematic and independent control over surface reactivity and electric field strength would accelerate the discovery of highly active electrocatalysts for these reactions by providing a means of reducing the transition state energy through field stabilization. Herein, we demonstrate that intermetallic alloying enables independent and systematic control over d-band energetics and work function through the variation of alloy composition and oxophilic constituent identity, respectively. We identify several intermetallic phases exhibiting properties that should collectively yield higher intrinsic activity for CO reduction compared to conventional Cu-based electrocatalysts. However, we also highlight the propensity of these alloys to segregate in air as a significant roadblock to investigating their electrocatalytic activity

Ambient Pressure Hydrodesulfurization of Refractory Sulfur Compounds in Highly Sensitive μ‑Reactor Platform Coupled to a Time-of-Flight Mass Spectrometer

Tightened restrictions call for cleaner transportation fuels to minimize environmental and societal problems caused by the presence of sulfur in transportation fuels. This emphasizes the need for new and better catalysts in the field of hydrodesulfurization (HDS), which aims at removing the refractory sulfur from different petroleum streams mostly found in the form of the alkyl-substituted dibenzothiophenes (β-DBTs). In this work we demonstrate how a setup dedicated to testing minute amounts (nanogram) of well-defined catalytic systems in μ-reactors can be used in the gas-phase HDS of the model compounds DBT and 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the reaction pathways revealed by time-of-flight mass spectrometry. Specifically, we investigate HDS of DBT and 4,6-DMDBT on mass-selected Pt nanoparticles and show that only the direct desulfurization products are formed. The setup is a means to bridge the gap between structural characterization of model catalysts and their related activity in the HDS of DBT and 4,6-DMDBT

Using TiO₂ as a Conductive Protective Layer for Photocathodic H₂ Evolution

Surface passivation is a general issue for Si-based photoelectrodes because it progressively hinders electron conduction at the semiconductor/electrolyte interface. In this work, we show that a sputtered 100 nm TiO₂ layer on top of a thin Ti metal layer may be used to protect an n⁺p Si photocathode during photocatalytic H₂ evolution. Although TiO₂ is a semiconductor, we show that it behaves like a metallic conductor would under photocathodic H₂ evolution conditions. This behavior is due to the fortunate alignment of the TiO₂ conduction band with respect to the hydrogen evolution potential, which allows it to conduct electrons from the Si while simultaneously protecting the Si from surface passivation. By using a Pt catalyst the electrode achieves an H₂ evolution onset of 520 mV vs NHE and a Tafel slope of 30 mV when illuminated by the red part (λ > 635 nm) of the AM 1.5 spectrum. The saturation photocurrent (H₂ evolution) was also significantly enhanced by the antireflective properties of the TiO₂ layer. It was shown that with proper annealing conditions these electrodes could run 72 h without significant degradation. An Fe²⁺/Fe³⁺ redox couple was used to help elucidate details of the band diagram

Electroreduction of CO on Polycrystalline Copper at Low Overpotentials

Cu is the only monometallic electrocatalyst to produce highly reduced products from CO₂ selectively because of its intermediate binding of CO. We investigate the performance of polycrystalline Cu for the electroreduction of CO in alkaline media (0.1 M KOH) at low overpotentials (−0.4 to −0.6 V vs RHE). We find that polycrystalline Cu is highly active at these potentials. The overall CO reduction rates are comparable to those of the nanostructured forms of the material, albeit with a distinct product distribution. While nanostructured forms of Cu favor alcohols, polycrystalline Cu produces greater amounts of C₂ and C₃ aldehydes, as well as ethylene

Engineering Ni–Mo–S Nanoparticles for Hydrodesulfurization

Nanoparticle engineering for catalytic applications requires both a synthesis technique for the production of well-defined nanoparticles and measurements of their catalytic performance. In this paper, we present a new approach to rationally engineering highly active Ni–Mo–S nanoparticle catalysts for hydrodesulfurization (HDS), i.e., the removal of sulfur from fossil fuels. Nanoparticle catalysts are synthesized by the sputtering of a Mo₇₅Ni₂₅ metal target in a reactive atmosphere of Ar and H₂S followed by the gas aggregation of the sputtered material into nanoparticles. The nanoparticles are filtered by a quadrupole mass filter and subsequently deposited on a planar substrate, such as a grid for electron microscopy or a microreactor. By varying the mass of the deposited nanoparticles, it is demonstrated that the Ni–Mo–S nanoparticles can be tuned into fullerene-like particles, flat-lying platelets, and upright-oriented platelets. The nanoparticle morphologies provide different abundances of Ni–Mo–S edge sites, which are commonly considered the catalytically important sites. Using a microreactor system, we assess the catalytic activity of the Ni–Mo–S nanoparticles for the HDS of dibenzothiophene. The measurements show that platelets are twice as active as the fullerene-like particles, demonstrating that the Ni–Mo–S edges are more active than basal planes for the HDS. Furthermore, the upright-standing orientation of platelets show an activity that is six times higher than the fullerene-like particles, demonstrating the importance of the edge site number and accessibility to reducing, e.g., sterical hindrance for the reacting molecules

Protection of p⁺‑n-Si Photoanodes by Sputter-Deposited Ir/IrO_<i>x</i> Thin Films

Sputter deposition of Ir/IrO_<i>x</i> on p⁺-n-Si without interfacial corrosion protection layers yielded photoanodes capable of efficient water oxidation (OER) in acidic media (1 M H₂SO₄). Stability of at least 18 h was shown by chronoamperomety at 1.23 V versus RHE (reversible hydrogen electrode) under 38.6 mW/cm² simulated sunlight irradiation (λ > 635 nm, AM 1.5G) and measurements with quartz crystal microbalances. Films exceeding a thickness of 4 nm were shown to be highly active though metastable due to an amorphous character. By contrast, 2 nm IrO_<i>x</i> films were stable, enabling OER at a current density of 1 mA/cm² at 1.05 V vs. RHE. Further improvement by heat treatment resulted in a cathodic shift of 40 mV and enabled a current density of 10 mA/cm² (requirements for a 10% efficient tandem device) at 1.12 V vs. RHS under irradiation. Thus, the simple IrO_<i>x</i>/Ir/p⁺-n-Si structures not only provide the necessary overpotential for OER at realistic device current, but also harvest ∼100 mV of free energy (voltage) which makes them among the best-performing Si-based photoanodes in low-pH media

CO₂ Electroreduction on Well-Defined Bimetallic Surfaces: Cu Overlayers on Pt(111) and Pt(211)

We have studied the electrochemical reduction of CO₂ on Cu overlayers on Pt(111) and Pt(211) surfaces. These systems were chosen to investigate the effect of strain on the catalytic activity of Cu surfaces and to obtain information about the role of steps in this process. The selectivity toward hydrocarbons on the copper overlayers is much lower than on polycrystalline copper due to a higher selectivity for hydrogen evolution. With the aim of understanding the lower activity toward CO₂ electroreduction of the Cu overlayers, we also studied the surfaces under reaction condition using electrochemical scanning tunneling microscopy (EC-STM). In the presence of CO, the Cu overlayer changes from a flat to a granular structure exposing part of the Pt surface. The exposed Pt surface accounts for the high selectivity of these structures toward hydrogen evolution. These results illustrate the dynamic nature of the surface under reaction conditions and that <i>in situ</i> measurements are crucial to understand catalytic activity