Water-energy Nexus: Studies On Salinity Gradient Energy Harvest And Desalination

Water and energy are fundamentally linked, and both are important for the development of human society. The demand for renewable energy and freshwater are two global challenges in the 21st century. Herein, a novel chloride-ion (Cl−) concentration flow cell (CFC) based on two symmetrical electrodes (BiCl3, CoCl2, VCl3, or BiOCl) separately by a cation-exchange membrane was used as an efficient method to recover salinity gradient (SG) energy. The CFC with metal chloride electrodes (BiCl3, CoCl2, and VCl3) was based on Cl− extraction/insertion, and that with the BiOCl electrodes was depended on Cl– intercalation/deintercalation. Similarly, the facile designed MnOx/biochar composite was also demonstrated as an efficient alternative for efficient SG energy recovery using CFC based on Na+ intercalation/deintercalation. The CFC with MnOx/biochar electrodes possessed the highest power density of 5.67 W m-2, which was higher than those of most previous methods for SG energy harvest. At the presence of other inorganic ions (K+, Mg2+, Ca2+, and SO42-) in feed solutions, both the open circuit voltage and power density were inhibited, indicating that pretreatment would be needed to obtain better power output when using natural feed waters. In addition, the BiOCl electrode was also proved to be an alternative and efficient anion-capturing/releasing electrode in capacitive mixing (CapMix) for SG energy recovery. The polyelectrolytes coated mixing entropy battery (MEB) were comparable and even higher than those with AgCl anionic electrodes. Besides, both the graphene oxide (GO) and carbon nanotube (CNT) were successfully introduced to the matrix of poly(acrylic acid-co-acrylamide) hydrogel for SG energy harvest depended on the swelling and shrinking under freshwater and seawater. The results suggested that GO/CNT hybrid hydrogel can be used for efficient SG energy harvest. Lastly, a membrane-free capacitive deionization (CDI) cell was constructed with MnO2 and polypyrrole grafted activated carbon (Ppy/AC) electrodes, which can reversibly and selectively intercalate Na+ (MnO2) and Cl- (Ppy/AC) ions because of the faradaic pseudocapacitive behaviours. Both the salt removal capacity and salt removal rate of the Ppy/AC-MnO2 cell were higher than reported conventional CDI, membrane-CDI and hybrid-CDI, suggesting the Ppy/AC-MnO2 CDI cell can be an efficient desalination method

Boosted brackish water desalination and water softening by facilely designed MnO2/hierarchical porous carbon as capacitive deionization electrode

Capacitive deionization (CDI) is a promising technique for brackish water desalination. However, its salt electrosorption capacity is insufficient for practical application yet, and little information is available on hardness ion (Mg2+, Ca2+) removal in CDI. Herein, hierarchical porous carbon (HPC) was prepared from low-cost and renewable microalgae via a simple one-pot approach, and both MnO2/HPC and polyaniline/HPC (PANI/HPC) composites were then synthesized using a facile, one-step hydrothermal method. Compared with the MnO2 electrode, the MnO2/HPC electrode presented an improved hydrophilicity, higher specific capacitance, and lower electrode resistance. The electrodes exhibited pseudocapacitive behaviors, and the maximum salt electrosorption capacities of MnO2/HPC-PANI/HPC CDI cell was up to 0.65 mmol g−1 NaCl, 0.71 mmol g−1 MgCl2, and 0.76 mmol g−1 CaCl2, respectively, which were comparable and even higher than those of the previously reported CDI cells. Additionally, the MnO2/HPC electrode presented a selectivity order of Ca2+ ≥ Mg2+ > Na+, and the divalent cation selectivity was found to be attributed to their stronger binding strength in the cavity of MnO2. Multiscale simulations further reveal that the MnO2/HPC electrodes with the unique luminal configuration of MnO2 and HPC as supportive framework could offer a great intercalation selectivity of the divalent cations and exhibit a great promise in hardness ion removal

Mo2N nanobelt cathodes for efficient hydrogen production in microbial electrolysis cells with shaped biofilm microbiome

High cost platinum (Pt) catalysts limit the application of microbial electrolysis cells (MECs) for hydrogen (H) production. Here, inexpensive and efficient MoN nanobelt cathodes were prepared using an ethanol method with minimized catalyst and binder loadings. The chronopotentiometry tests demonstrated that the MoN nanobelt cathodes had similar catalytic activities for H evolution compared to that of Pt/C (10 wt%). The H production rates (0.39 vs. 0.37 m-H/m/d), coulombic efficiencies (90% vs. 77%), and overall hydrogen recovery (74% vs. 70%) of MECs with the MoN nanobelt cathodes were also comparable to those with Pt/C cathodes. However, the cost of MoN nanobelt catalyst ($31/m) was much less than that of Pt/C catalysts ($ 1930/m). Furthermore, the biofilm microbiomes at electrodes were studied using the PacBio sequencing of full-length 16S rRNA gene. It indicated Stenotrophomonas nitritireducens as a putative electroactive bacterium dominating the anode biofilm microbiomes. The majority of dominant species in the MoN and Pt/C cathode communities belonged to Stenotrophomonas nitritireducens, Stenotrophomonas maltophilia, and Comamonas testosterone. The dominant populations in the cathode biofilms were shaped by the cathode materials. This study demonstrated MoN nanobelt catalyst as an alternative to Pt catalyst for H production in MECs

Influence of load frequency and corrosive environments on fatigue behavior of as-extruded Mg–Zn–Zr–Nd alloy

Fatigue resistance is a key criterion for new material that would be applied as an implant. As a “smart” implant material with good biodegradability and high strength, Mg–2Zn–0.5Zr–0.5Nd alloy has been recognized as a promising candidate for bone implant. A series of tests on fatigue properties of extruded Mg–2Zn–0.5Zr–0.5Nd alloy are carried out in this study. Alternating cyclic dynamic loads at frequencies of 5 Hz and 10 Hz both in air and in 0.9 wt% NaCl solution were loaded on extruded Mg–2Zn–0.5Zr–0.5Nd alloy respectively. In air condition, the fatigue life variational trends of Mg–2Zn–0.5Zr–0.5Nd alloy at different frequencies are similar according to the stress-life (S–N) curves. However, under high fatigue cycles, the lower loading frequency prolongs the loading time of repetitive stresses and reduces the fatigue life of the samples. In 0.9 wt% NaCl solution, the S–N curves under different frequencies show different changing trends due to the synergistic effect of corrosion environment and loading frequency. It is also found that the fatigue resistance of the alloy in 0.9 wt% NaCl solution is poorer than that in air due to the significant promotion of the formation and growth of corrosion pits by the NaCl environment. In addition, according to the fatigue fracture morphology analysis, it can be found that the failed samples show different fracture patterns in air and 0.9 wt% NaCl solution

Site selection of desert solar farms based on heterogeneous sand flux

Abstract Site selection for building solar farms in deserts is crucial and must consider the dune threats associated with sand flux, such as sand burial and dust contamination. Understanding changes in sand flux can optimize the site selection of desert solar farms. Here we use the ERA5-Land hourly wind data with 0.1° × 0.1° resolution to calculate the yearly sand flux from 1950 to 2022. The mean of sand flux is used to score the suitability of global deserts for building solar farms. We find that the majority of global deserts have low flux potential (≤ 40 m3 m-1 yr-1) and resultant flux potential (≤ 2.0 m3 m-1 yr-1) for the period 1950–2022. The scoring result demonstrates that global deserts have obvious patchy distribution of site suitability for building solar farms. Our study contributes to optimizing the site selection of desert solar farms, which aligns with the United Nations sustainability development goals for achieving affordable and clean energy target by 2030