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•Methanol solution is suitable as antifreeze for freeze-thaw cycling of PEMFC MEAs.•Antifreeze eliminates performance losses due to freezing for j < 1.6 A cm−2.•Antifreeze allows ...PEMFC operation at sub-zero temperatures during cold-start.
One challenge for polymer electrolyte membrane fuel cells (PEMFCs) for electric vehicles is to ensure cold start capability and longevity under freeze-thaw (F/T) cycling. Today, PEMFCs undergo dry gas purging to remove residual water before a cold shut-down to avoid degradation due to icing. This study investigates an alternative procedure with alcohol-water solution as antifreeze. In order to demonstrate the suitability of methanol as antifreeze, F/T cycling tests using methanol have been compared with conventional dry gas purging of the cell before F/T cycling. The results show that performance degradation upon F/T cycling is mitigated when flooding the cell with the antifreeze prior to F/T cycling. Specifically, performance losses are observed at high current densities only and the peak performance of the cell does not decrease. Moreover, cold start procedures are examined to allow a start-up of the cell after being soaked with the antifreeze. In this context it is found that PEMFC operation is possible at sub-zero temperature if residual methanol is in the cell. However, residual methanol decreases power density during cold start. Hence, methanol needs to be removed from the cell by reaction or by prolonged water purging to reach nominal power.
This work provides single cell durability tests of membrane electrode assemblies in dynamic operation regularly interrupted by recovery procedures for the removal of reversible voltage losses. ...Degradation rates at different loads in one single test can be determined from these tests. Hence, it is possible to report degradation rates versus current density instead of a single degradation rate value. A clear discrimination between reversible and irreversible voltage loss rates is provided. The irreversible degradation rate can be described by a linear regression of voltage values after the recovery steps. Using voltage values before refresh is less adequate due to possible impacts of reversible effects. The reversible contribution to the voltage decay is dominated by an exponential decay after restart, eventually turning into a linear one. A linear-exponential function is proposed to fit the reversible voltage degradation. Due to this function, the degradation behavior of an automotive fuel cell can be described correctly during the first hours after restart. The fit parameters decay constant, exponential amplitude and linear slope are evaluated. Eventually, the reasons for the voltage recovery during shutdown are analyzed showing that ionomer effects in the catalyst layer and/or membrane seem to be the key factor in this process.
•Discrimination between reversible and irreversible degradation.•Determination of voltage loss rates at different loads in a single durability test.•Quantitative evaluation of reversible voltage decay by linear-exponential function.•Recovery of reversible voltage losses by shutdown recovery procedure.
Abstract
Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount ...in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr
2
CaIrO
6
achieves 10 mA cm
−2
at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO
6
octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr
2
CaIrO
6
as anode and low Ir loading (0.4 mg
Ir
cm
−2
). The cell achieves 2.40 V at 6 A cm
−2
(overload) and no loss in performance at a constant 2 A cm
−2
(nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.
Aims
Physical and psychiatric comorbidities are common in cancer patients and could impact their treatment and prognosis. However, the evidence base regarding the influence of comorbidities in the ...management and health service use of patients is still scant. In this research we investigated how physical comorbidities are related to the mental health and help‐seeking of cancer patients.
Methods
Data were obtained from the representative National Health Survey of Spain (2017). Participants were respondents who reported a cancer diagnosis (n = 484). These were also matched with controls without cancer history (n = 484) based on age, gender, and region. Four alternative physical comorbidities indices were created based on information regarding 28 chronic conditions. Outcomes of interest were psychological distress and having consulted a mental healthcare professional in the year before the survey.
Results
Thirty percent of cancer patients reported significant psychological distress but only 10% had consulted a professional. After adjusting for sociodemographic variables, among cancer patients each additional comorbidity was associated with 9% higher odds of reporting high psychological distress (odds ratio OR = 1.09, 95% confidence interval CI: 1.01–1.16) and 21% higher odds of having consulted a mental healthcare professional (OR = 1.21, 95% CI: 1.09–1.34). The effects of comorbidities depended on the type of index and were different in controls without cancer history.
Conclusion
Physical comorbidities in cancer patients are associated with higher risk of psychological distress and higher demand for mental health services. We encourage further research on this issue as it could improve mental health screening and management in oncologic care.
Abstract
The production of green hydrogen in water electrolyzers is limited by the oxygen evolution reaction (OER). State-of-the-art electrocatalysts are based on Ir. Ru electrocatalysts are a ...suitable alternative provided their performance is improved. Here we show that low-Ru-content pyrochlores (R
2
MnRuO
7
, R = Y, Tb and Dy) display high activity and durability for the OER in acidic media. Y
2
MnRuO
7
is the most stable catalyst, displaying 1.5 V at 10 mA cm
−2
for 40 h, or 5000 cycles up to 1.7 V. Computational and experimental results show that the high performance is owed to Ru sites embedded in RuMnO
x
surface layers. A water electrolyser with Y
2
MnRuO
7
(with only 0.2 mg
Ru
cm
−2
) reaches 1 A cm
−2
at 1.75 V, remaining stable at 200 mA cm
−2
for more than 24 h. These results encourage further investigation on Ru catalysts in which a partial replacement of Ru by inexpensive cations can enhance the OER performance.
Nanoelectromechanical resonators have potential applications in sensing, cooling, and mechanical signal processing. An important parameter in these systems is the strength of coupling the resonator ...motion to charge transport through the device. We investigated the mechanical oscillations of a suspended single-walled carbon nanotube that also acts as a single-electron transistor. The coupling of the mechanical and the charge degrees of freedom is strikingly strong as well as widely tunable (the associated damping rate is approximately 3 x 10⁶ Hz). In particular, the coupling is strong enough to drive the oscillations in the nonlinear regime.
Proton exchange membrane water electrolysis (PEMWE) technology is especially advantageous for green H2 production as a clean energy vector. During the water electrolysis process, the oxygen evolution ...reaction (OER) requires a large amount of iridium (2‐3 mgIr cm−2) as catalyst. This material is scarce and expensive, representing a major bottleneck for large‐scale deployment of electrolyzers. This work develops an anode with 10‐fold reduction of Ir loading (0.2 mgIr cm−2) compared to what it is used in commercial PEMWE for more than 1000 h. An advanced catalyst based on an Ir mixed oxide (Sr2CaIrO6) is used for this purpose. Transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), and X‐ray absorption spectroscopy (XAS) analyses show that the unconventional structure of the reconstructed catalyst can contribute to the reduction of Ir in the catalyst layer. The reconfiguration of the ionomer in the catalyst layer is also observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), results in almost the full coverage of the catalytic layer with ionomer. The results presented herein demonstrate that it is possible to achieve high performance and stability in PEMWE with low Ir loading in the anode without showing significant degradation.
A double perovskite catalyst Sr2CaIrO6 reduces the amount of iridium significantly in the anode for proton exchange membrane water electrolyzers (PEMWE). High performance and durability can be achieved with only 0.2 mgIr cm‐2. Anodes with low iridium loadings can be established as the new state of the art in PEMWEs making green hydrogen more economically attractive.
The determination of trace elements using stripping voltammetry may be seriously affected by the presence of intensive matrix background or interfering peaks, leading to poorer detection limits ...and/or inaccurate quantitative results. In this work, we have tested the use of signal transformation (e.g., second derivative) in the analysis of platinum in seawater and sediment digests by means of catalytic adsorptive stripping voltammetry. In natural waters, the limit of detection of Pt is affected by a broad background wave due to the formazone complex used in the sample matrix for its determination, while in sediment digests, the Pt peak may be interfered with due to the presence of elevated concentrations of Zn, affecting the accuracy of the determination. Results applying second derivative signal transformation revealed a significant improvement (2–3-fold) of the detection limit in water due to the minimization of background effects, therefore allowing shorter accumulation times and faster determinations. In the presence of interfering peaks, the inaccuracy resulting from erroneous baseline selection in the original signal is eliminated when the second derivative is used. Signal processing should be considered as a useful tool for other voltammetric methodologies where more accurate or faster determinations are needed.
Miniaturization of electronic circuits into the single-atom level requires novel approaches to characterize transport properties. Due to its unrivaled precision, scanning probe microscopy is regarded ...as the method of choice for local characterization of atoms and single molecules supported on surfaces. Here we investigate electronic transport along the anisotropic germanium (001) surface with the use of two-probe scanning tunneling spectroscopy and first-principles transport calculations. We introduce a method for the determination of the transconductance in our two-probe experimental setup and demonstrate how it captures energy-resolved information about electronic transport through the unoccupied surface states. The sequential opening of two transport channels within the quasi-one-dimensional Ge dimer rows in the surface gives rise to two distinct resonances in the transconductance spectroscopic signal, consistent with phase-coherence lengths of up to 50 nm and anisotropic electron propagation. Our work paves the way for the electronic transport characterization of quantum circuits engineered on surfaces.
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•Novel Fe/N/C electrocatalysts for ORR in acid media based in iron-containing porous organic polymers from non-expensive dicyanobenzenes (DCB).•1,2-DCB lead to more active catalysts ...than 1,4-DCB, because vicinal N atoms in 1,2-DCB are more prone to coordinate to one Fe atom as FeNx moieties.•The ORR activity is boosted by the presence of FeNx moieties.
In this work, we report the synthesis of Fe/N/C electrocatalysts using triazine based porous organic polymers as precursors. Iron-doped triazine porous organic polymers were obtained by in situ polymerization of iron precursor and 1,2- or 1,4- dicyanobenzene (DCB). In order to obtain the actual catalyst, the polymer obtained was subjected to thermal treatment under NH3. The catalysts obtained exhibit activity and durability for the oxygen reduction reaction in acid electrolyte. Thorough characterization of the catalysts reveal the formation of several types of iron species, including metallic iron, iron carbides and Fe-Nx moieties. The latter species is the main responsible for the high activity measured for the oxygen reduction reaction in acid electrolyte. 1,2-DCB results in more active catalysts than 1,4-DCB due to the higher fraction of FeNx ensembles in the former, probably because vicinal positions of N-bearing groups are more prone to coordinate Fe atoms.
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