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

Limitations of Electrochemical Nitrogen Oxidation toward Nitrate

The electrocatalytic N2 oxidation reaction (NOR) using renewable electricity is a promising alternative to the industrial synthesis of nitrate from NH3 oxidation. However, breaking the triple bond in the nitrogen molecule is one of the most essential challenges in chemistry. In this work, we use density functional theory simulations to investigate the plausible reaction mechanisms of electrocatalytic NOR and its competition with oxygen evolution reaction (OER) at the atomic scale. We focus on the electrochemical conversion of inert N2 to active *NO during NOR. We propose formation of *N2O from *N2 and *O as the rate-determining step (RDS). Following the RDS, a microkinetic model is utilized to study the rate of NOR on metal oxides. Our results demonstrate that a lower activation energy is obtained when a catalyst binds *O weakly. We show that the reaction is extremely challenging but also that design strategies have been suggested to promote electrochemical NOR

Intermetallic Alloys as CO Electroreduction CatalystsRole of Isolated Active Sites

One of the main challenges associated with the electrochemical CO or CO₂ reduction is poor selectivity toward energetically rich products. In order to promote selectivity toward hydrocarbons and alcohols, most notably, the hydrogen evolution reaction (HER) should be suppressed. To achieve this goal, we studied intermetallic compounds consisting of transition metal (TM) elements that can reduce CO (Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) separated by TM and post transition metal elements (Ag, Au, Cd, Zn, Hg, In, Sn, Pb, Sb, and Bi) that are very poor HER catalysts. In total, 34 different stable binary bulk alloys forming from these elements have been investigated using density functional theory calculations. The electronic and geometric properties of the catalyst surface can be tuned by varying the size of the active centers and the elements forming them. We have identified six different potentially selective intermetallic surfaces on which CO can be reduced to methanol at potentials comparable to or even slightly positive than those for CO/CO₂ reduction to methane on Cu. Common features shared by most of the selective alloys are single TM sites. The role of single sites is to block parasitic HER and thereby promote CO reduction

A Linear Response DFT+<i>U</i> Study of Trends in the Oxygen Evolution Activity of Transition Metal Rutile Dioxides

There are known errors in oxidation energies of transition metal oxides caused by an improper treatment of their d-electrons. The Hubbard <i>U</i> is the computationally cheapest addition one can use to capture correct reaction energies, but the specific Hubbard <i>U</i> oftentimes must be empirically determined only when suitable experimental data exist. We evaluated the effect of adding a calculated, linear response <i>U</i> on the predicted adsorption energies, scaling relationships, and activity trends with respect to the oxygen evolution reaction for a set of transition metal dioxides. We find that applying a <i>U</i> greater than zero always causes adsorption energies to be more endothermic. Furthermore, the addition of the Hubbard <i>U</i> greater than zero does not break scaling relationships established without the Hubbard <i>U</i>. The addition of the calculated linear response <i>U</i> value produces shifts of different systems along the activity volcano that results in improved activity trends when compared with experimental results

Supporting data for: A linear response, DFT+U study of trends in the oxygen evolution activity of transition metal rutile dioxides

<p>This directory contains all of the finished calculations required for fully analysis of the paper "A linear response, DFT+U study of trends in the oxygen evolution activity of transition metal rutile dioxides" by Zhongnan Xu, Jan Rossmeisl, and John R Kitchin. To use this repository, download the supporting information file and run the scripts present in either 'supporting-information.pdf' or 'supporting-information.org'.</p> <p>The is the release of the supporting data before the first submission to the first journal.</p

Bridging the Catalyst Reactivity Gap between Au and Cu for the Reverse Water–Gas Shift Reaction

The reverse water–gas shift reaction (rWGSR) is highly relevant for CO2 utilization in sustainable fuel and chemical production. Both Au and Cu are interesting for rWGSR catalysis, but it turns out that the reactivities of Au and Cu are very different. In this study, we consider alloys made from Au, Ag, Cu, Pt, and Pd to identify surfaces with reactivities for CO2 dissociation between Cu(111) and Au(111). Additionally, interesting alloy surfaces should have activation energies for CO2 dissociation that are only a little higher than the endothermic reaction energy. We find that certain Cu-based alloys with Ag and Au meet these criteria, whereas alloys containing Pt or Pd do not. The low additional cost in activation energy occurs when the transition-state and final-state configurations are made to look very similar due to the placement of the different metal elements on the surface. Finally, we construct a kinetic model that compares the rate of the rWGSR to the estimated rate of unwanted side reactions (i.e., methane formation or coking) on Ag–Cu alloy surfaces with varying compositions and random placement of the Ag and Cu atoms. The thermodynamics favor methane formation over rWGSR, but the model suggests that Ag–Cu alloy surfaces are highly selective for the rWGSR

Unifying the 2e^– and 4e^– Reduction of Oxygen on Metal Surfaces

Understanding trends in selectivity is of paramount importance for multi-electron electrochemical reactions. The goal of this work is to address the issue of 2e^– versus 4e^– reduction of oxygen on metal surfaces. Using a detailed thermodynamic analysis based on density functional theory calculations, we show that to a first approximation an activity descriptor, Δ<i>G</i>_OH*, the free energy of adsorbed OH*, can be used to describe trends for the 2e^– and 4e^– reduction of oxygen. While the weak binding of OOH* on Au(111) makes it an unsuitable catalyst for the 4e^– reduction, this weak binding is optimal for the 2e^– reduction to H₂O₂. We find quite a remarkable agreement between the predictions of the model and experimental results spanning nearly 30 years

Naravne oblike gibanja kot sredstvo razvoja moči v mali odbojki (10-12 let)

RuO₂ has been reported to reduce CO₂ electrochemically to methanol at low overpotential. Herein, we have used density functional theory (DFT) to gain insight into the mechanism for CO₂ reduction on RuO₂(110). We have investigated the thermodynamic stability of various surface terminations in the electrochemical environment and found CO covered surfaces to be particularly stable, although their formation might be kinetically limited under mildly reducing conditions. We have identified the lowest free energy pathways for CO₂ reduction to formic acid (HCOOH), methanol (CH₃OH), and methane (CH₄) on partially reduced RuO₂(110) covered with 0.25 and 0.5 ML of CO*. We have found that CO₂ is reduced to formic acid, which is further reduced to methanol and methane. At 0.25 ML of CO*, the reduction of formate (OCHO*) to formic acid is the thermodynamically most difficult step and becomes exergonic at potentials below −0.43 V vs the reversible hydrogen electrode (RHE). On the other hand, at 0.5 ML of CO*, the reduction of formic acid to H₂COOH* is the thermodynamically most difficult step and becomes exergonic at potentials below −0.25 V vs RHE. We have found that CO₂ reduction activity on RuO₂ changes with CO coverage, which suggests that CO coverage can be used as a tool to tune the CO₂ reduction activity. We have shown the mechanism for CO₂ reduction on RuO₂ to be different from that on Cu. On Cu, hydrocarbons are formed at high Faradaic efficiency through reduction of CO* at ∼1 V overpotential, while on RuO₂, methanol and formate are formed through reduction of formic acid at lower overpotentials. Using our understanding of the CO₂ reduction mechanism on RuO₂, we suggest reduction of formic acid on RuO₂, which should lead to methanol and methane production at relatively low overpotentials

The Influence of Inert Ions on the Reactivity of Manganese Oxides

Inert ion doping is a possible method to modify electrical conductivity and catalytic activity of transition-metal oxide electrocatalysts. Despite the importance of dopants, little is known about the underlying mechanisms for the change of the system properties. We have performed density functional theory calculations to investigate the influence of different valent ions on the O₂ evolution reaction activity of β-MnO₂ and Mn₂O₃. While Mn₂O₃ is unaffected by dopants, β-MnO₂ is strongly affected by ions placed in a subsurface position. Doping does not affect the ion charge at the active site, but instead it effects the bond character. This is concluded through an analysis of the density overlap regions indicator and the density of states showing that the partially covalent nature of the bonds in β-MnO₂ is responsible for the changes in the adsorbate binding energies. This mechanism is not active in the mostly ionic Mn₂O₃. These results highlight the need to explicitly consider the detailed bonding situation and to go beyond simple charge transfer considerations when describing doping of transition metal oxide catalysts

Insight into Selectivity Differences of Glycerol Electro-Oxidation on Pt(111) and Ag(111)

Electro-oxidation is a way to utilize glycerol, a byproduct of biodiesel production, to produce fuels and feedstock chemicals for the chemical industry. A significant challenge is to get products with high selectivity, so it is desirable to understand the glycerol oxidation mechanisms in further detail. Using density functional theory calculations, we investigated possible glycerol oxidation intermediates on Pt(111) and Ag(111). We find that the different adsorption preferences of the intermediates on Pt (adsorption via carbon atoms) and Ag (adsorption via oxygen atoms) lead to different preferred reaction pathways, resulting in different products. The reaction pathways on both surfaces involve glyceraldehyde as a key intermediate; however, upon further oxidation, Pt(111) preferentially produces glyceric acid (CH2OH–CHOH–COOH), while on Ag(111) C–C bonds are broken, which leads to the production of glycolaldehyde and formic acid (CH2OH–CHO and HCOOH). These predictions agree well with the experimental outcome of the electro-oxidation of glycerol on Pt and Ag surfaces. Our study therefore provides useful insights for optimizing the selectivity of glycerol oxidation and improving the utilization of glycerol