Exploring efficient and low‐cost electrocatalysts for the oxygen‐reduction reaction (ORR) and oxygen‐evolution reaction (OER) is critical for developing renewable energy technologies such as fuel ...cells, metal–air batteries, and water electrolyzers. A rational design of a catalyst can be guided by identifying descriptors that determine its activity. Here, a descriptor study on the ORR/OER of spinel oxides is presented. With a series of MnCo2O4, the Mn in octahedral sites is identified as an active site. This finding is then applied to successfully explain the ORR/OER activities of other transition‐metal spinels, including MnxCo3−xO4 (x = 2, 2.5, 3), LixMn2O4 (x = 0.7, 1), XCo2O4 (X = Co, Ni, Zn), and XFe2O4 (X = Mn, Co, Ni). A general principle is concluded that the eg occupancy of the active cation in the octahedral site is the activity descriptor for the ORR/OER of spinels, consolidating the role of electron orbital filling in metal oxide catalysis.
The eg occupancy of the active cation in octahedral sites is identified as the descriptor that governs the activity of the oxygen‐reduction reaction and the oxygen‐evolution reaction on transition‐metal spinel oxides.
Exploring efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is critical for developing anion exchange membrane electrolyzers. The key to a rational ...catalyst design is understanding the descriptors that govern the alkaline HER activity. Unfortunately, the principles that govern the alkaline HER performance remain unclear and are still under debate. By studying the alkaline HER at a series of NiCu bimetallic surfaces, where the electronic structure is modulated by the ligand effect, we demonstrate that alkaline HER activity can be correlated with either the calculated or the experimental-measured d band center (an indicator of hydrogen binding energy) via a volcano-type relationship. Such correlation indicates the descriptor role of the d band center, and this hypothesis is further supported by the evidence that combining Ni and Cu produces a variety of adsorption sites, which possess near-optimal hydrogen binding energy. Our finding broadens the applicability of d band theory to activity prediction of metal electrocatalysts and may offer an insightful understanding of alkaline HER mechanism.
Abstract
Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to ...manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxide
FM
/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1
st
dehydrogenation to reduce the barrier for subsequent O-O coupling.
The proton exchange membrane (PEM) water electrolysis is one of the most promising hydrogen production techniques. The oxygen evolution reaction (OER) occurring at the anode dominates the overall ...efficiency. Developing active and robust electrocatalysts for OER in acid is a longstanding challenge for PEM water electrolyzers. Most catalysts show unsatisfied stability under strong acidic and oxidative conditions. Such a stability challenge also leads to difficulties for a better understanding of mechanisms. This review aims to provide the current progress on understanding of OER mechanisms in acid, analyze the promising strategies to enhance both activity and stability, and summarize the state‐of‐the‐art catalysts for OER in acid. First, the prevailing OER mechanisms are reviewed to establish the physicochemical structure–activity relationships for guiding the design of highly efficient OER electrocatalysts in acid with stable performance. The reported approaches to improve the activity, from macroview to microview, are then discussed. To analyze the problem of instability, the key factors affecting catalyst stability are summarized and the surface reconstruction is discussed. Various noble‐metal‐based OER catalysts and the current progress of non‐noble‐metal‐based catalysts are reviewed. Finally, the challenges and perspectives for the development of active and robust OER catalysts in acid are discussed.
Developing proton exchange membrane water electrolyzers requires a fundamental understanding of the oxygen evolution reaction (OER) in acid, which is the primary focus of this review. The water electrolyzer in alkaline and acid are compared; and the recent advances in OER mechanisms, the strategies for enhancing activity and stability of electrocatalysts, surface reconstruction, and the state‐of‐the‐art electrocatalysts are discussed.
High-altitude hypoxia (reduced inspired oxygen tension due to decreased barometric pressure) exerts severe physiological stress on the human body. Two high-altitude regions where humans have lived ...for millennia are the Andean Altiplano and the Tibetan Plateau. Populations living in these regions exhibit unique circulatory, respiratory, and hematological adaptations to life at high altitude. Although these responses have been well characterized physiologically, their underlying genetic basis remains unknown. We performed a genome scan to identify genes showing evidence of adaptation to hypoxia. We looked across each chromosome to identify genomic regions with previously unknown function with respect to altitude phenotypes. In addition, groups of genes functioning in oxygen metabolism and sensing were examined to test the hypothesis that particular pathways have been involved in genetic adaptation to altitude. Applying four population genetic statistics commonly used for detecting signatures of natural selection, we identified selection-nominated candidate genes and gene regions in these two populations (Andeans and Tibetans) separately. The Tibetan and Andean patterns of genetic adaptation are largely distinct from one another, with both populations showing evidence of positive natural selection in different genes or gene regions. Interestingly, one gene previously known to be important in cellular oxygen sensing, EGLN1 (also known as PHD2), shows evidence of positive selection in both Tibetans and Andeans. However, the pattern of variation for this gene differs between the two populations. Our results indicate that several key HIF-regulatory and targeted genes are responsible for adaptation to high altitude in Andeans and Tibetans, and several different chromosomal regions are implicated in the putative response to selection. These data suggest a genetic role in high-altitude adaption and provide a basis for future genotype/phenotype association studies necessary to confirm the role of selection-nominated candidate genes and gene regions in adaptation to altitude.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
► The catalytic effect of platinum on carbon corrosion in PEFCs was investigated. ► Platinum catalyzes the carbon corrosion reaction. ► Catalytic effect depends on the upper and lower limit of the ...applied potential pulses. ► Formation of a platinum oxide layer has a passivating effect.
To assess the catalytic effect of platinum on the corrosion of the high surface area carbon support, single triangular potential sweeps with various upper and lower limits were applied to fuel cells comprising electrodes having different Pt/C compositions. Carbon loss rates in H
2/N
2 and air/air mode were determined by integration of the resulting CO
2 concentration peaks in the exhaust gas of the positive electrode. Generally, the contribution of platinum catalyzed carbon corrosion to total CO
2 evolution was found to decrease with increasing upper potential limit. Similar carbon loss rates obtained for Pt/C and pure carbon electrodes in case of lower potential limits of 1.0
V indicate that the catalytic activity of platinum is substantially lowered by the formation of a passivating oxide layer on the platinum particles. Changes in corrosion behavior in the potential range below 0.6
V, which cannot be attributed to platinum effects, are suggested to originate from modifications in carbon surface oxide composition. Due to the high oxygen equilibrium potential of approximately 1
V, carbon corrosion in air/air mode is significantly influenced by platinum oxide formation. However, the polarization of the negative electrode and the influence of platinum oxidation on the equilibrium potential results in a passivating effect that is less pronounced than expected from measurements in H
2/N
2 mode.
A rational design for oxygen evolution reaction (OER) catalysts is pivotal to the overall efficiency of water electrolysis. Much work has been devoted to understanding cation leaching and surface ...reconstruction of very active electrocatalysts, but little on intentionally promoting the surface in a controlled fashion. We now report controllable anodic leaching of Cr in CoCr2O4 by activating the pristine material at high potential, which enables the transformation of inactive spinel CoCr2O4 into a highly active catalyst. The depletion of Cr and consumption of lattice oxygen facilitate surface defects and oxygen vacancies, exposing Co species to reconstruct into active Co oxyhydroxides differ from CoOOH. A novel mechanism with the evolution of tetrahedrally coordinated surface cation into octahedral configuration via non‐concerted proton‐electron transfer is proposed. This work shows the importance of controlled anodic potential in modifying the surface chemistry of electrocatalysts.
CoCr2O4 activated at 1.7 V for 1.5 h (Act‐CoCr2O4) exhibits better OER activity compared to IrO2 in alkaline solutions. Pristine CoCr2O4 is originally inactive; activation (>1.56 V) promotes Cr leaching and lattice oxygen losses in CoCr2O4, leaving the highly defective surface for Co species to reconstruct into octahedrally coordinated Co3+–4+ oxyhydroxide.
Background
Preventive measures to decrease the frequency and intensity of anaphylactic events are essential to provide optimal care for allergic patients. Aggravating factors may trigger or increase ...the severity of anaphylaxis and therefore need to be recognized and avoided.
Objective
To identify and prioritize factors associated with an increased risk of developing severe anaphylaxis.
Methods
Data from the Anaphylaxis Registry (122 centers in 11 European countries) were used in logistic regression models considering existing severity grading systems, elicitors, and symptoms to identify the relative risk of factors on the severity of anaphylaxis.
Results
We identified higher age and concomitant mastocytosis (OR: 3.1, CI: 2.6‐3.7) as the most important predictors for an increased risk of severe anaphylaxis. Vigorous physical exercise (OR: 1.5, CI: 1.3‐1.7), male sex (OR: 1.2, CI: 1.1‐1.3), and psychological burden (OR: 1.4, CI: 1.2‐1.6) were more often associated with severe reactions. Additionally, intake of beta‐blockers (OR: 1.9, CI: 1.5‐2.2) and ACE‐I (OR: 1.28, CI: 1.05, 1.51) in temporal proximity to allergen exposition was identified as an important factor in logistic regression analysis.
Conclusion
Our data suggest it may be possible to identify patients who require intensified preventive measures due to their relatively higher risk for severe anaphylaxis by considering endogenous and exogenous factors.
During the lifetime of a polymer electrolyte fuel cell, the pore structure of the Pt/C catalyst layer may change as a result of carbon corrosion. Three-dimensional visualization of porosity changes ...is important to understand the origin of fuel cell performance deterioration. A focused ion beam/scanning electron microscopy (FIB/SEM) approach was adopted together with electron tomographic studies to visualize the three-dimensional pore structure of a Pt/C catalyst. In the case of pristine catalyst layers, the pores form an interconnected network. After 1000 start-up/shut-down cycles, severe carbon corrosion leads to a collapse of the support structure. The porosity of the degraded catalyst layer shrinks drastically, resulting in a structure of predominantly isolated pores. These porosity changes hinder the mass transport in the catalyst layer, consequently leading to a substantial loss of fuel cell performance. FIB/SEM serial sectioning and electron tomography allows three-dimensional imaging of the catalyst pore structure, which is a prerequisite for modeling and optimizing mass transport in catalyst layers.
Nanoparticles are key components in the advancement of future energy technologies, thus, strategies for preparing nanoparticles in large volume by techniques that are cost‐effective are required. In ...the substitution of fossil‐fuels by renewable energy resources, nanometer‐sized particles play a key role for synthesizing energy vectors from varying and heterogeneous biomass feedstocks. They are extensively used in reformers for the production of hydrogen from solid, liquid, or gaseous energy carriers. Catalyst activities depend critically on their size‐dependent properties. Nanoparticles are further indispensable as electrocatalysts in fuel cells and other electrochemical converters. The desire to increase the activity per unit area, and decrease the necessary amount of the expensive catalytic standard, platinum, has spurred innovative approaches for the synthesis of platinum‐alloy nanoparticles by wet chemistry, colloidal routes, or physical techniques such as sputtering.
Made to measure: Nanostructuring of surfaces is important for the activity of catalysts in the conversion of fuels and in electrochemistry. Particular care must be taken to ensure the optimal particle size in the nanometer range. The picture shows a new method for the colloidal synthesis of platinum and platinum‐alloy nanoparticles of defined dimensions.
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