Given that a considerably large population suffers from shortage of water, there are numerous on‐going efforts to turn seawater into freshwater, and electrochemical desalination ...processes—particularly capacitive deionization (CDI)—have gained significant attention due to their high energy efficiency and reliable performance. Meanwhile, carbonaceous electrode materials, which are most commonly used in CDI systems, have poor long‐term stability due to unfavorable interactions with oxygen in saline water. Herein, rapid and vigorous inversion of surface charges in heteroatom‐doped carbon electrodes, which leads to a robust operation of CDI with high desalination capacity, is reported for the first time. By carbonization of coffee wastes, nitrogen‐ and sulfur‐codoped activated carbon with hierarchical micro/mesopores are prepared in an environmentally‐friendly manner, and this carbon results in a significantly higher inverted capacity than that of various activated carbon counterparts in long‐term CDI operations, without any sign of drop in performance. Investigations on the changes in physicochemical properties of the electrodes during the inversion disclose the favorable roles of nitrogen and sulfur dopants, which can be summarized as enlarging the difference between the surface charges of the two electrodes by chemical interactions with oxygen in the anode and carbon in the cathode.
Heteroatom‐doped carbon electrodes undergo rapid inversion of surface charges during capacitive deionization, which leads to high desalination capacity and excellent long‐term stability. The roles of dopants in accelerated inversion are revealed as having a direct interaction with oxygen in the anode and carbon in the cathode, and this discovery provides important insights for design of carbonaceous materials for various electrochemical applications.
The influence of heat treatment on the microstructure, mechanical properties, and wear behaviors of stainless steel 316L (SS316L) produced via selective laser melting (SLM) was investigated. The ...fabricated SLM samples were subjected to two different heat treatments: a typical furnace-type heat treatment conducted at 1100 °C for 0.5 h and hot isostatic pressing performed at 1100 °C and 100 MPa for 1.5 h. High-density SLM samples with low porosities were obtained by increasing the laser power and decreasing the scan speed. The heat treatments of the fabricated SLM samples induced the removal of porosity, cellular microstructure, and dense dislocation structures with a slight increase in grain size. In terms of mechanical properties, the fabricated SLM samples exhibited similar hardness and tensile strength properties to those of the conventional SS316L, while a significantly lower elongation was evident. The heat treatments of the fabricated SLM samples improved elongation, while the surface hardness and tensile strength decreased owing to microstructural evolution. During the pin-on-disk test, the conventional SS316L and fabricated SLM sample exhibited similar wear resistance values, which decreased after the heat treatments of the fabricated SLM samples owing to the heat treatment-induced surface softening.
Electrochemical water splitting is one of the most promising approaches for sustainable energy conversion and storage toward a future hydrogen society. This demands durable and affordable ...electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we report the preparation of uniform Ni-P-O, Ni-S-O, and Ni-S-P-O electrocatalytic films on nickel foam (NF) substrates
via
flow cell-assisted electrodeposition. Remarkably, electrodeposition onto 12 cm
2
substrates was optimized by strategically varying critical parameters. The high quality and reproducibility of the materials is attributed to the use of a 3D-printed flow cell with a tailored design. Then, the as-fabricated electrodes were tested for overall water splitting in the same flow cell under alkaline conditions. The best-performing sample, NiSP/NF, required relatively low overpotentials of 93 mV for the HER and 259 mV for the OER to produce a current density of 10 mA cm
−2
. Importantly, the electrodeposited films underwent oxidation into amorphous nickel (oxy)hydroxides and oxidized S and P species, improving both HER and OER performance. The superior electrocatalytic performance of the Ni-S-P-O films originates from the unique reconstruction process during the HER/OER. Furthermore, the overall water splitting test using the NiSP/NF couple required a low cell voltage of only 1.85 V to deliver a current density of 100 mA cm
−2
. Overall, we demonstrate that high-quality electrocatalysts can be obtained using a simple and reproducible electrodeposition method in a robust 3D-printed flow cell.
A reproducible and efficient electrodeposition method in a 3D-printed flow cell is used to synthesize high-quality Ni-S-P-O films on nickel foam for overall water splitting.
Abstract
This study investigates the sensitivity of the boreal winter prediction skill of Community Atmosphere Model 5 to the choice of the dynamical core. Both finite volume (FV) and spectral ...element (SE) dynamical cores are tested. An additional FV with the SE topography (FV
SE
) is also conducted to isolate the possible influence of the topography. The three dynamical core experiments, which ran from 2001/2002–2017/2018, are validated using Japanese 55 year reanalysis data. It turns out that the SE (−4.27 °C) has a smaller cold bias in boreal-winter surface air temperature (SAT) than the FV (−5.17 °C) and FV
SE
(−5.29 °C), particularly in North America, East Asia, and Southern Europe/Northern Africa. Significant North Atlantic Oscillation-like biases are also identified in the mid-troposphere. These biases affect seasonal prediction skills. Although the overall prediction skills of boreal-winter SAT, quantified by the anomaly correlation coefficient (ACC), and root-mean-square error (RMSE), are reasonably good (ACC = 0.40 and RMSE = 0.47 in the mean values of SE, FV, and FV
SE
), they significantly differ from one region to another, depending on the choice of dynamical cores. For North America and Southern Europe/Northern Africa, SE shows better skills than FV
SE
and FV. Conversely, in East Asia, FV and FV
SE
outperform SE. These results suggest that the appropriate choice of the dynamical cores and the bottom boundary conditions could improve the boreal-winter seasonal prediction on a regional scale.
To achieve practically high electrocatalytic performance for the oxygen evolution reaction (OER), the active surface area should be maximized without severely compromising electron and mass transport ...throughout the catalyst electrode. Though the importance of electron and mass transport has been studied using low surface area catalysts under low current densities (∼tens of mA/cm2), the transport properties of large surface area catalysts under high operating current densities (∼500 mA/cm2) for practical OER catalysis have rarely been explored. Herein, three-dimensional (3D) hierarchically porous anodized nickel foams (ANFs) with large and variable surface areas were synthesized via electrochemical anodization of 3D nickel foam and applied as OER electrocatalysts in Fe-free and unpurified KOH electrolytes. Using Fe-free and in situ Fe-doped ANF that were prepared in Fe-free and unpurified electrolytes, respectively, we investigated the interdependent effects of active surface area and transport properties on OER activity under practically high current densities. While activity increased linearly with active surface area for Fe-free ANF, the activity of Fe-doped ANF showed a nonlinear increase with active surface area due to lower electrocatalytic activity enhancement. Detailed investigations on the possible factors (Fe incorporation, mass transport, and electron transport) identified that electron transport limitations played the major role in restricting the activity enhancement with increasing active surface area for Fe-doped ANF, although Fe-doped ANF has electron transport properties better than those of Fe-free ANF. This study exemplifies the growing significance of electron transport properties in large surface area catalysts, especially those with superb intrinsic catalytic activity and high operating current density.
AlGaN/GaN FinMISHFETs with m-plane sidewall surface channel and various fin widths (W fin ) were fabricated and characterized. The investigated devices have much higher current drivability due to the ...uniform and smooth surface of m-plane than those with the a-plane sidewall surface channel. The AlGaN/GaN FinMISHFETs with Wfin smaller than 36 nm exhibit normally-off operation, high Ion/Ioff ratio of 108, and remarkable subthresholdswing (SS) smaller than 40 mV/decade in the wide current range of at least three orders. Combined with a positive threshold voltage, SS values smaller than 60 mV/decade in a wide current rage of at least three orders are among the world's best subthreshold characteristics. Furthermore, when W fin is 31 nm, the off-state drain current is as low as 10-12 A. We show that this sharp switch is due to the simultaneous turn-on of the 2-D electron gas and the m-plane sidewall surface channel. The simulation results are carried out to show the gate-induced variation of the electron concentration within the fin structure, and the assumption of considering gate width as a function of gate bias is also developed to explain the reason for deep sub-60mV/decade in the demonstrated devices.
Dye-sensitized solar cells (DSSCs) are highly efficient and reliable photovoltaic devices that are based on nanostructured semiconductor photoelectrodes. From their inception in 1991, colloidal TiO2 ...nanoparticles (NPs) with the large surface area have manifested the highest performances and the particle size of around 20 nm is generally regarded as the optimized condition. However, though there have been reports on the influences of particle sizes in conventional DSSCs employing iodide redox electrolyte, the size effects in DSSCs with the state-of-the-art cobalt electrolyte have not been investigated. In this research, systematic analyses on DSSCs with cobalt electrolytes are carried out by using various sizes of NPs (20–30 nm), and the highest performance is obtained in the case of 30 nm sized TiO2 NPs, indicating that there is a reversed power conversion efficiency trend when compared with those with the iodide counterpart. Detailed investigations on various factorslight harvesting, charge injection, dye regeneration, and charge collectionreveal that TiO2 particles with a size range of 20–30 nm do not have a notable difference in charge injection, dye regeneration, and even in light-harvesting efficiency. It is experimentally verified that the superior charge collection property is the sole origin of the higher performance, suggesting that charge collection should be prioritized for designing nanostructured TiO2 photoelectrodes for DSSCs employing cobalt redox electrolytes.
Polyhydroxyalkanoate (PHA) is a biodegradable plastic that can be used to replace petroleum-based plastic. In addition, as a medium-chain-length PHA (mcl-PHA), it can be used to provide elastomeric ...properties in specific applications. Because of these characteristics, recently, there has been much research on mcl-PHA production using inexpensive biomass materials as substrates. In this study, mcl-PHA producers were screened using alkanes (n-octane, n-decane, and n-dodecane) as sources of carbon. The amount of PHA produced by Pseudomonas resinovorans using sole n-octane, n-decane, or n-dodecane was 0.48 g/L, 0.27 g/L, or 0.07 g/L, respectively, while that produced using mixed alkane was 0.74 g/L. As a larger amount of PHA was produced using mixed alkane compared with sole alkane, a statistical mixture analysis was used to determine the optimal ratio of alkanes in the mixture. The optimal ratio predicted by the analysis was a medium with 9.15% n-octane, 6.44% n-decane, and 4.29% n-dodecane. In addition, through several concentration-specific experiments, the optimum concentrations of nitrogen and phosphorus for cell growth and maximum PHA production were determined as 0.05% and 1.0%, respectively. Finally, under the determined optimal conditions, 2.1 g/L of mcl-PHA and 60% PHA content were obtained using P. resinovorans in a 7 L fermenter.
Boosting hydrogen evolution reaction (HER) performance in alkaline media has been a topic of interest in a world that continuously strives for cleaner energy conversion systems. The paucity of ...protons provides a challenge to performing the HER in an alkaline environment and is a major impediment to decreasing the energy requirement needed to produce hydrogen. Here, we improve the HER activity of nickel-nitride by electrochemically anodizing the surface which aids water dissociation in alkaline HER. We experimentally show that by oxidizing the nickel nitride on a nickel foam (Ni
3
N/NF) surface using cyclic voltammetry (CV) cycles in Fe-unpurified KOH media, Ni
3
N can be converted to a Ni(OH)
2
/Ni
3
N composite. Activation of the Ni
3
N/NF with 50 CV cycles resulted in a low HER overpotential of 172 and 207 mV at the current densities of 50 and 100 mA cm
−2
, respectively. The 50 CV cycle Ni
3
N/NF also had the minimum charge transfer resistance at 6 Ω compared to all other prepared samples, and the Tafel slope is 100.87 mV dec
−1
.
The impact of
in situ
electrooxidation in a Ni
3
N electrocatalyst on its hydrogen evolution activity and electrochemical stability was investigated in alkaline media.
Understanding how electrode materials evolve in energy conversion and storage devices is critical to optimizing their performance. We report a comprehensive investigation into the impact of
in situ
...metal incorporation on nickel oxyhydroxide oxygen evolution reaction (OER) electrocatalysts, encompassing four multivalent cations: Fe, Co, Mn, and Cu. We found that adding trace amounts of these cations to alkaline electrolytes alters the electrocatalytic and energy storage properties of NiO
x
H
y
films after electrochemical conditioning. As opposed to the well-known increase in OER activity induced by Fe,
in situ
incorporation of trace Co and Mn cations increases the total capacitance, while Cu incorporation does not proceed. We show that increasing Fe and Co concentrations leads to a maximum electrochemical performance attributed to a saturation threshold in the metal uptake. Depth profiling measurements reveal that metal incorporation is confined to the surface of the film, resulting in an interstratified structure that partially retains the more active, disordered phase at the surface. Building upon solid-state chemistry principles, we provide an in-depth discussion of four critical factors determining the occurrence of
in situ
metal incorporation, underscoring its nature as a cation exchange process. To further support this concept, we manipulate cation exchange by shifting the solubility equilibrium and
via
ion complexation. By providing a better understanding of
in situ
metal incorporation, our results underscore its potential as a strategy for manipulating the surface chemical composition, thus advancing the development of electrochemical energy materials.
Trace metal cations dissolved in alkaline electrolytes incorporate into nickel hydroxide/oxyhydroxide through
in situ
cation exchange, creating an interstratified structure near the surface of the material that impacts the electrochemical performance.
