Effects of postpartum fatigue, parenting stress, and family support on postpartum depression in Chinese first-time mothers: a cross-sectional study.

PURPOSE: This study aimed to explore the levels of postpartum fatigue, parenting stress, family support, and postpartum depression (PPD) experienced by first-time Chinese mothers and to investigate their impact on PPD. METHODS: This cross-sectional survey involved 150 primigravida women attending postnatal checkups in Hebi City, Henan Province, China. Demographic data and information on environmental variables (living conditions, family relationships), postpartum fatigue, parenting stress, family support (expected vs. actual level), and PPD were collected. RESULTS: The average age of the women was 26.25 years (SD, ±3.90), with 78.7% at risk for PPD (score ≥10). Significant correlations were found between PPD and postpartum fatigue (r=.63, p<.001), parenting stress (r=.59, p<.001), and family support (r=.40, p<.001). In model 1, which examined the influence of women's demographic variables on PPD, significant factors included a poor relationship with parents (ß=.24, p=.001), a poor relationship with parents-in-law (ß=.18, p=.029), and a poor relationship with the husband (ß=.20, p=.013). When the three research variables were incorporated into model 2, the factors contributing to a higher level of PPD included a poor relationship with parents-in-law (ß=.14, p=.033), increased postpartum fatigue (ß=.37, p<.001), increased parenting stress (ß=.33, p<.001), and less family support than expected (ß=.12, p=.048). CONCLUSION: The most critical factors influencing PPD include postpartum fatigue, parenting stress, poor relationships with parents-in-law, and low family support among Chinese primiparas. To mitigate PPD levels, healthcare professionals should screen mothers for depression in outpatient clinics and offer education and counseling to both mothers and their families or companions regarding PPD.

Psychometric testing of the Chinese version of the Perinatal Infant Care Social Support tool: a methodological study.

PURPOSE: This study aimed to translate the Perinatal Infant Care Social Support (PICSS) instrument into Chinese and to verify the reliability and validity of the translated version. METHODS: This study used a cross-sectional design to examine the reliability and validity of the Chinese version of the PICSS (C-PICSS). A cohort of 150 first-time mothers in China participated, attending hospital follow-up care at 6 weeks postpartum. Data were collected after obtaining informed consent from the mothers. RESULTS: The majority of mothers were aged between 20 and 29 years, with a mean age of 26.25 (±3.90) years. An item analysis of the 19 items in the C-PICSS showed that all items had an item-total score correlation above 0.2. This resulted in a Kaiser-Meyer-Olkin value of 0.92 and a significant Bartlett's test of sphericity (χ2=1,778.65, p<.001), confirming the suitability of the data for factor analysis. Correlation analyses revealed a strong positive relationship between infant care social support and general social support (r=.62, p<.001), and a negative relationship between infant care social support and postpartum depression (r=-.38, p<.001). Higher scores for infant care social support were associated with reporting positive relationships with their husbands (t=3.72, p<.001) and high levels of spousal involvement (t=4.09, p<.001). In terms of structural support, spouses were identified as the primary source. CONCLUSION: The research results indicate that C-PICSS is reliable and valid as an indicator of social support for infant care among Chinese mothers.

High-pressure study of a 3d-4f heterometallic CuEu-organic skeleton.

We prepared a 3d-4f heterobimetallic CuEu-organic framework NBU-8 with a density of 1921 kg m-3 belonging to the family of dense packing materials (dense metal-organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu2+ and Eu3+ as the metal centres; the molecular formula is Cu3Eu2(PBA)6(NO3)6·H2O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10-2) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch-Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu-BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol-1. The present work will provide fresh ideas for the study of mechanical energy in other materials.

In Situ Exfoliation Growth Strategy Realizing Controlled Synthesis of 3D to 2D MOF Materials as High-Performance Electrochemical Biosensors.

Two-dimensional (2D) metal-organic framework (MOF) nanosheets with large surface area, ultrathin thickness, and highly accessible active sites have attracted great research attention. Developing efficient approaches to realize the controllable synthesis of well-defined 2D MOFs with a specific composition and morphology is critical. However, it is still a significant challenge to construct thin and uniform 2D MOF nanosheets and resolve the reagglomeration as well as poor stability of target 2D MOF products. Here, an "in situ exfoliation growth" strategy is proposed, where a one-step synthetic process can realize the successful fabrication of PBA/MIL-53(NiFe)/NF nanosheets on the surface of nickel foam (NF) via in situ conversion and exfoliation growth strategies. The PBA/MIL-53(NiFe)/NF nanosheets combine the individual advantages of MOFs, Prussian blue analogues (PBAs), and 2D materials. As expected, the resulting PBA/MIL-53(NiFe)/NF as a glucose electrode exhibits an extremely high sensitivity of 25.74 mA mM-1 cm-2 in a very wide concentration range of 180 nM to 4.8 µM. The present exciting work provides a simple and effective strategy for the construction of high-performance nonenzymatic glucose electrochemical biosensors.

Quality evaluation of pregnancy-related mobile applications in South Korea: a descriptive study.

PURPOSE: This study aimed to describe the characteristics of mobile applications (apps) related to pregnancy in South Korea and evaluate their quality. METHODS: We conducted a systematic search for pregnancy-related apps available in Korea in two app stores as of April 29, 2022. The quality of apps was assessed using the Korean translation of the Mobile Application Rating Scale for objective quality with four subdomains (engagement, function, aesthetics, and information) and four items for subjective quality. RESULTS: In total, 163 apps were selected and reviewed. Both the objective and subjective quality of the apps were found to be desirable, with scores exceeding 3 out of 5 (range, 34-82). All subdomain scores in the objective quality assessment were also desirable. Among the four objective quality subdomains, aesthetics received the highest scores, followed by information, function, and engagement. In terms of subjective quality, the scores for a comprehensive overall evaluation, continuous use, and recommendation exceeded 3 out of 5, with the exception of payment. Only a small number of apps (n=4, 2.9%) were backed by a reliable authority, such as an expert review. Significant differences were observed in the objective quality of apps across different content categories (F=3.86, p=.003). CONCLUSION: Most pregnancy-related apps had desirable levels of objective and subjective quality. However, app content experts seldom provide reviews. It is crucial for nurses to recommend apps to expectant mothers that offer dependable content, regularly updated with the latest information.

(FeMnCe)-co-doped MOF-74 with significantly improved performance for overall water splitting.

Developing inexpensive electrocatalysts with high activity and stability is of great value for overall water splitting. In this work, we designed a series of 3d-4f (FeMnCe)-trimetallic MOF-74 with different ratios of 3d- and 4f-metal centers. Among them, FeMn6Ce0.5-MOF-74/NF exhibited the best electrocatalytic performance for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline solution. It only requires a low overpotential of 281 mV@100 mA cm-2 for OER and 186 mV@-10 mA cm-2 for HER in 1 M KOH. With FeMn6Ce0.5-MOF-74/NF as the anode and cathode in the overall water splitting system, only 1.65 V is needed to deliver a current density of 10 mA cm-2. In particular, for the as-fabricated FeMn6Ce0.5-MOF-74/NF||Pt/C cell unit, only 1.40 V is needed to achieve 10 mA cm-2. Therefore, the successful design of 3d-4f mixed-metallic MOF-74 provides a new viewpoint to develop highly efficient non-precious metal electrocatalysts.

One-step synthesis of 2D@3D hollow Prussian blue analogue as a high-performance bifunctional electrochemical sensor.

Prussian blue analogues (PBAs) are a family of classic coordination polymers. They have been widely applied in various fields including electrochemical sensors. Cubic nanoparticle structure is their common morphology. It is still a great challenge to design a hollow and two-dimensional (2D) PBA material. Of course, it will be a significant surprise if a hollow cube and 2D sheet can be integrated into one material. In this work, we designed a simple one-step synthetic strategy and resolved the above difficulty, wherein a hollow cubic PBA covered by 2D ultrathin nanosheets was successfully constructed, namely hollow tremella-like PBA (HTPBA). Furthermore, Ni foam (NF) as a substrate was introduced to obtain a self-supporting HTPBA/NF-12 electrode. HTPBA/NF-12, as a bifunctional electrochemical sensor electrode, exhibited distinguished catalytic performance towards glucose and nitrite, including remarkable selectivity, reproducibility, sensitivity for glucose (21 410 µA mM-1 cm-2) and nitrite (1248 µA mM-1 cm-2), wide linear range of 2-1250 µM and 5-3380 µM, along with low detection limit of 0.056 µM and 0.38 µM, respectively. More importantly, HTPBA/NF-12 electrodes possessed good reusability and practicability even in goat serum. In this study, we developed a simple and effective strategy to fabricate 2D@3D PBA material with excellent electrocatalytic activity and provide a totally new viewpoint in the PBA sensing field.

UiO-66-Derived PBA Composite as Multifunctional Electrochemical Non-Enzymatic Sensor Realizing High-Performance Detection of Hydrogen Peroxide and Glucose.

In this work, a highly efficient multifunctional non-enzymatic electrochemical sensor is successfully fabricated based on a facile two-step synthetic strategy. It resolves two important challenges of poor stability and low reproducibility compared to conventional electrochemical enzyme-based sensors. Herein, a metal-organic framework (UiO-66) is selected as a sacrificial template to construct the corresponding Prussian blue analogue (PBA) target to improve its stability and conductivity, namely, PBA/UiO-66/NF. Target PBA/UiO-66/NF exhibits excellent electrochemical sensing performance as hydrogen peroxide (H2O2) and glucose sensors with ultrahigh sensitivity of up to 1903 µA mM-1 cm-2 for H2O2 and 22,800 µA mM-1 cm-2 for glucose, as well as a very low detection limit of 0.02 µM (S/N = 3) for H2O2 and 0.28 µM for glucose. Especially, extremely high stability can be observed, which will be beneficial for practical application.

Iron-Cobalt-Cerium Multimetallic Oxides Derived from Prussian Blue Precursors: Enhanced Oxygen Evolution Electrocatalysis.

Exploring non-precious metal-based electrocatalysts is still challenging in 21st century. In this work, a series of hexagonal bipyramidal Ce-based PBA materials as precursors with different Fe/Co metal ratios, namely as CeFex Co1-x -PBA, are successfully constructed via co-precipitation method and converted into corresponding metal oxides (denoted as Fex Co1-x CeOy ) via thermal treatment. Then, they as electrocatalysts realize highly efficient oxygen evolution reaction (OER). Especially, as-synthesized Fe0.7 Co0.3 CeOy electrocatalyst shows very low overpotentials of 320 mV at the current density of 10 mA cm-2 and the Tafel slop of 98.4 mV dec-1 in 1 M KOH with remarkable durability for 24 h, which was due to the synergistic effect of multi-metal FeCoCe centers. Furthermore, a two-electrode cell of Fe0.7 Co0.3 CeOy /NF||Pt/C/NF realizes outstanding overall water splitting with a voltage of only 1.71 V at 10 mA cm-2 and remarkable long-term durability, that is even superior to benchmark IrO2 /NF||Pt/C/NF counterpart.

Vanadium-Based Trimetallic Metal-Organic-Framework Family as Extremely High-Performing and Ultrastable Electrocatalysts for Water Splitting.

This is the first time that the pore-space-partition (PSP) strategy is being successfully applied in the electrochemical field for water splitting, realizing the highly efficient construction of a series of ultrastable pristine MOF electrocatalysts. On integrating the vanadium-based trimetallic building cluster (M2V), the target M2V-MOFs exhibit excellent electrocatalytic activity for HER, OER, and water splitting. In particular, ultralow overpotentials of 314 and 198 mV for Fe2V-MOF as OER and HER electrocatalysts, respectively, can drive a current density of 10 mA cm-2. The fabricated Fe2V-MOF||Pt/C two-electrode configuration for the overall water splitting yields a current density of 10 mA cm-2 at only 1.6 V vs RHE, which is superior to that of the commercial IrO2||Pt/C couple. Notably, high structural and chemical stabilities still can be observed in alkaline condition. This work opens up an exciting pathway to design efficient and stable electrocatalysts based on pristine MOF by integrating the PSP strategy and multimetallic centers.

Molecular Regulation Based on Functional Trimetallic Metal-Organic Frameworks for Efficient Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) as classic crystalline porous materials have attracted great interest in the catalytic field. However, how to realize molecular regulation of the MOF structure to achieve a remarkable oxygen evolution reaction (OER) electrocatalyst is still a challenge. Herein, we designed several series of special MOF materials to explore the relationship between the structure and properties as well as the related reactive mechanism. First, various metal centers, including Fe, Co, Ni, Zn, and Mg, were utilized to construct the first series of trimetallic MOF materials, namely, M3-MOF-BDC, where BDC = 1,4-benzenedicarboxylic acid, also known as terephthalic acid. Among of them, Fe3-MOF-BDC shows the best OER performance and only needs an overpotential of 312 mV at 10 mA cm-2. Then, functional BDC-X ligands (X = NH2, OH, NO2, DH) with various characteristic groups were selected to construct a new series, namely, Fe3-MOF-BDC-X, to further improve its OER electrocatalytic performance. As expected, Fe3-MOF-BDC-NH2 exhibited a greatly enhanced OER performance with ultralow Tafel slopes of 45 mV dec-1 and overpotentials of 280 mV at 10 mA cm-2 when the BDC-NH2 ligand was adopted, even superior to commercial IrO2 (323 mV) and most of the reported pristine MOFs as OER electrodes. Much higher structural stability was proven. The detailed structure-property relationship and mechanism are discussed. In a word, this work provides a very important theoretical basis for the design and exploration of new MOF electrocatalysts.

Indium-Based Metal-Organic Framework for Efficient Photocatalytic Hydrogen Evolution.

In this work, an indium-based metal-organic framework was successfully constructed, namely, as In-MOF, by elaborately selecting an InIII center with unique properties and a functional tetracarboxylic acid with unsaturated and open-coordinated nodes. Interestingly, the InIII center was connected to a single-metal-node-based porous three-dimensional pts net. Its structure was dentified by single-crystal and powder X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, etc. Considering the special luminescent characteristic of an indium-based framework, as-prepared In-MOF was explored as a photocatalyst for H2 production from water splitting. The testing results demonstrate that In-MOF as a promising photocatalyst with a suitable band gap realizes a H2 evolution efficiency of 777.65 µmol g-1 h-1.

Synthesis and Applications of Prussian Blue and Its Analogues as Electrochemical Sensors.

Prussian blue (PB) and its analogue (PBA) are a kind of representative cyanide-based coordination polymer. They have received enormous research interest and have shown promising applications in the electrochemical sensing field due to their excellent electrochemical activity and unique structural characteristics including open framework structure, high specific surface area, and adjustable metal active sites. In this review, we summarize the latest research progress of PB/PBA as an electrochemical sensor in detail from three aspects: fabrication strategy, synthesis method and electrochemical sensor application. For the fabrication strategy, we discussed different fabrication methods containing the combination of PBA and carbon materials, metal nanoparticles, polymers, etc., respectively, as well as their corresponding sensing mechanism for improving performance. We also presented the synthesis methods of PB/PBA materials in detail, such as: coprecipitation, hydrothermal and electrodeposition. In addition, the effects of different methods on the morphology, particle size and productivity of PB/PBA materials are also concluded. For the application of electrochemical sensors, the latest progress of such materials as electrochemical sensors for glucose, H2 O2 , toxic compounds, and biomolecules have been summarized. Finally, we conclude remaining challenges of PB/PBA-based materials as electrochemical sensors, and provide personal perspectives for future research in this field.

MOF-Derived Bimetallic CoFe-PBA Composites as Highly Selective and Sensitive Electrochemical Sensors for Hydrogen Peroxide and Nonenzymatic Glucose in Human Serum.

The fabrication of two-dimensional (2D) metal-organic frameworks (MOFs) and Prussian blue analogues (PBAs) combines the advantages of 2D materials, MOFs and PBAs, resolving the poor electronic conductivity and slow diffusion of MOF materials for electrochemical applications. In this work, 2D leaflike zeolitic imidazolate frameworks (Co-ZIF and Fe-ZIF) as sacrificial templates are in situ converted into PBAs, realizing the successful fabrication of PBA/ZIF nanocomposites on nickel foam (NF), namely, CoCo-PBA/Co-ZIF/NF, FeFe-PBA/Fe-ZIF/NF, CoFe-PBA/Co-ZIF/NF, and Fe/CoCo-PBA/Co-ZIF/NF. Such fabrication can effectively reduce transfer resistance and greatly enhance electron- and mass-transfer efficiency due to the electrochemically active PBA particles and NF substrate. These fabricated electrodes as multifunctional sensors achieve highly selective and sensitive glucose and H2O2 biosensing with a very wide detective linear range, extremely low limit of detection (LOD), and good stability. Among them, CoFe-PBA/Co-ZIF/NF exhibits the best sensing performance with a very wide linear range from 1.4 µM to 1.5 mM, a high sensitivity of 5270 µA mM-1 cm-2, a low LOD of 0.02 µM (S/N = 3), and remarkable stability and selectivity toward glucose. What is more, it can realize excellent detection of glucose in human serum, demonstrating its practical applications. Furthermore, this material as a multifunctional electrochemical sensor also manifests superior detection performance against hydrogen peroxide with a wide linear range of 0.2-6.0 mM, a high sensitivity of 196 µA mM-1 cm-2, and a low limit of detection of 1.08 nM (S/N = 3). The sensing mechanism for enhanced performance for glucose and H2O2 is discussed and proved by experiments in detail.

Iron-Based Metal-Organic Framework System as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions.

The fabrication of highly efficient and sustainable electrocatalysts used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is exceedingly challenging and warranted for overall water splitting. In this work, we successfully synthesized a series of metal-organic frameworks (MOFs), namely, as Fe2M-MOF (M = Fe, Co, Ni, Zn, Mn; H4L = 3,3,5,5'-azoxybenzenetetracarboxylic acid) under a simple and mild condition, in which the Fe3 cluster as a basic building unit was replaced by the second kind of metal center; at the same time, a redox-active organic linker was adopted. The Fe2M-MOF system as a multifunctional catalyst realizes great improvement of the OER and HER performances. Among of them, the Fe2Co-MOF catalyst exhibits an extremely low overpotential of 339 mV at a current density of 10 mA cm-2 and a very small Tafel slope of 36.2 mV dec-1 in an alkaline electrolyte for OER. This result has far exceeded the commercial catalyst IrO2. Meanwhile, Fe2Zn-MOF manifests excellent HER activity with a small overpotential of 221 mV at 10 mA cm-2 and a low Tafel slope of 174 mV dec-1. In addition, the good long-term stability for these catalysts can be evaluated under working conditions. Systematic investigations are used to explain the enhanced electrocatalytic mechanism. In conclusion, we provide a simple and effective strategy for the preparation of multifunctional catalysts for energy conversion applications based on a pristine MOF material with redox-active metal centers and organic linkers.

Rationally designed trimetallic Prussian blue analogues on LDH/Ni foam for high performance supercapacitors.

Rational design of a Prussian blue analogue (PBA)@Ni-Co layered double hydroxide (NiCo-LDH) nanocomposite electrode material is vitally important for synthesizing high-performance supercapacitor electrodes. In this work, such nanocomposite electrode materials were successfully fabricated by a facile hydrothermal method. Firstly, three-dimensional (3D) regulated NiCo-LDH nanosheets with high interlayer space were grown on nickel foam under mild synthetic conditions. Then these nanosheets as a precursor were in situ converted into the target PBA@NiCo-LDH/NF nanocomposite electrode by a facile thermal ion-exchange reaction with potassium ferricyanide (K3[Fe(CN)6]). A series of PBA@NiCo-LDH/NF nanocomposite electrodes were fabricated with different ratios of Ni and Co and reaction temperatures. Their structures and morphologies were characterized by X-ray diffraction (XRD), FT-IR and scanning electron microscopy (SEM). Electrochemical investigation reveals that the PBA@Ni0.4Co0.6-LDH electrode exhibits the best electrochemical performance with an area specific capacitance of 2004.26 mF cm-2 at 1 mA cm-2, which is much higher (about three times) than the properties of each single component. All results demonstrate that (1) high-performance composite electrodes can be effectively fabricated and (2) fabrication of such composites is highly necessary and important.

Zeolite-Type Metal Oxalate Frameworks.

While many metal oxalate salts are known, few are known to form zeolite-type topologies. The construction of zeolite types, especially those with low framework density such as RHO, from linear ligands is generally perceived as less likely, because the 180° metal-ligand-metal geometry deviates too much from the established strategy of using ligands with bent coordination geometry (centered around 145°) to mimic the geometry in natural zeolites. We show the general feasibility of using linear ligands for the synthesis of zeolite types by reporting a family of indium oxalate salts with multiple zeolite topologies, including RHO, GIS, and ABW. Of particular interest is the synthesis of a zeolite RHO net with double 8-rings and large alpha cages, which are highly desirable zeolite features.

The interlocked in situ fabrication of graphene@prussian blue nanocomposite as high-performance supercapacitor.

High-quality graphene@prussian blue (G@PB) nanocomposite sheets have been successfully fabricated via a one-step in situ hydrothermal method, in which uniform PB nanoparticles completely covered both sides of graphene sheets through control of the etching of the raw material and growth of the target products. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) demonstrated effective combination. A series of G@PB nanocomposite sheets with different graphene contents as well as other PB/carbonaceous composites and mixed G@PB materials provided adequate proof for the synergetic effect of graphene and Prussian blue in G@PB nanocomposite sheets as well as the important effect of each composite on the electrochemical performance; graphene not only prevented the agglomeration of PB nanoparticles but also provided conductive network for fast electron transport, which was verified by the IR voltage drop and EIS test. In particular, the G@PB-5 hybrid composite showed the highest capacitance of 388.09 F g-1 at a current density of 1 A g-1 and enhanced rate capability and long-term stability with 97.2% retention over 5000 cycles as well as coulombic efficiency of nearly 100%. Asymmetric supercapacitor cells were assembled by pairing an optimized nanocomposite electrode with an activated carbon negative electrode, which displayed a reversible operating voltage of 2.0 V. These high electrochemical performances render the G@PB-5 nanocomposite sheets promising for energy-storage hybrid electrodes.

A heterobimetallic metal-organic framework as a "turn-on" sensor toward DMF.

A non-luminescent 3d-4f heterobimetallic CuEu organic framework (NBU-8) was designedly synthesized with Cu2+ ions as a fluorescence quencher. NBU-8 as a sensor realized selective light recovery with a "turn-on" luminescence response toward N,N'-dimethylformamide (DMF) even in the presence of other amide molecules.

Hierarchical Two-Dimensional Conductive Metal-Organic Framework/Layered Double Hydroxide Nanoarray for a High-Performance Supercapacitor.

A novel hierarchical nanoarray material based on a two-dimensional metal-organic framework (Ni-CAT) and a layered double hydroxide (NiCo-LDH) was fabricated on a nickel foam substrate. By taking advantage of the regular nanostructure and making full use of the high porosity and excellent conductivity, the hybrid material exhibits a high areal capacitance for a supercapacitor (3200 mF cm-2 at 1 mA cm-2).