Characterizing the Impacts of Deposition Techniques on the Performance of MnO₂ Cathodes for Sodium Electrosorption in Hybrid Capacitive Deionization

Capacitive deionization (CDI) is currently limited by poor ion-selectivity and low salt adsorption capacity of porous carbon electrodes. To enhance selectivity and capacity via sodium insertion reactions, carbon aerogel electrodes were modified by depositing amorphous manganese dioxide layers via cyclic voltammetry (CV) and electroless deposition (ED). MnO₂-coated electrodes were evaluated in a hybrid capacitive deionization system to understand the relationship between oxide coating morphology, electrode capacitance, and sodium removal efficacy. Both deposition techniques increased electrode capacitance, but only ED electrodes improved desalination performance over bare aerogels. SEM imaging revealed ED deposition distributed MnO₂ throughout the aerogel, while CV deposition created a discrete crust, indicating that CV electrodes were limited by diffusion. Sodium adsorption capacity of ED electrodes increased with MnO₂ mass deposition, reaching a maximum of 0.77 mmol-Na⁺ per gram of cathode (2.29 mmol-Na⁺ g-MnO₂^–1), and peak charge efficiency of 0.95. The presence of MnO₂ also positively shifted the electrode potential window of sodium removal, reducing parasitic oxygen reduction and inverting the desalination cycle so that energy discharge coincides with salt removal (1.96 kg-NaCl kWh^–1). These results highlight the importance of deposition technique in improving desalination with MnO₂-coated electrodes

Extracellular Palladium Nanoparticle Production using Geobacter sulfurreducens

Sustainable methods are needed to recycle precious metals and synthesize catalytic nanoparticles. Palladium nanoparticles can be produced via microbial reduction of soluble Pd­(II) to Pd(0), but in previous tests using dissimilatory metal reducing bacteria (DMRB), the nanoparticles were closely associated with the cells, occupying potential reductive sites and eliminating the potential for cell reuse. The DMRB Geobacter sulfurreducens was shown here to reduce soluble Pd­(II) to Pd(0) nanoparticles primarily outside the cell, reducing the toxicity of metal ions, and allowing nanoparticle recovery without cell destruction that has previously been observed using other microorganisms. Cultures reduced 50 ± 3 mg/L Pd­(II) with 1% hydrogen gas (v/v headspace) in 6 h incubation tests [100 mg/L Pd­(II) initially], compared to 8 ± 3 mg/L (10 mM acetate) without H₂. Acetate was ineffective as an electron donor for palladium removal in the presence or absence of fumarate as an electron acceptor. TEM imaging verified that Pd(0) nanoparticles were predominantly in the EPS surrounding cells in H₂-fed cultures, with only a small number of particles visible inside the cell. Separation of the cells and EPS by centrifugation allowed reuse of the cell suspensions and effective nanoparticle recovery. These results demonstrate effective palladium recovery and nanoparticle production using G. sulfurreducens cell suspensions and renewable substrates such as H₂ gas

Amplifying Progress toward Multiple Development Goals through Resource Recovery from Sanitation

The United Nations’ Sustainable Development Goals (SDGs) recognize that current sanitation gaps must be closed to better serve those without access to safely managed systems (Target 6.2: universal sanitation coverage) and those connected to sewers without wastewater treatment (Target 6.3: halving the proportion of untreated wastewater). Beyond mitigating environmental and health concerns, implementing resource recovery sanitation systems could simultaneously improve the availability of agricultural nutrients (SDG 2) and household energy (SDG 7). This study estimates the potential for global, regional, and country-level resource recovery to impact nutrient and household electricity use through 2030. We distinguish impacts from newly installed sanitation systems (to achieve universal coverage), newly treated wastewater systems (to halve the proportion of untreated wastewater), and existing system replacement, while also considering urban and rural disparities and spatial colocation of nutrients with agricultural needs. This work points toward country-specific strategies for deriving the greatest benefit from sanitation investments while also identifying overarching trends to guide international research efforts. Globally, potential nutrient gains are an order of magnitude larger than electricity (a small fraction of total energy), and considerable impacts are possible in the least-developed countries, six of which could double or offset all projected nutrient and electricity use through newly installed sanitation systems

Hydrogen Generation in Microbial Reverse-Electrodialysis Electrolysis Cells Using a Heat-Regenerated Salt Solution

Hydrogen gas can be electrochemically produced in microbial reverse-electrodialysis electrolysis cells (MRECs) using current derived from organic matter and salinity-gradient energy such as river water and seawater solutions. Here, it is shown that ammonium bicarbonate salts, which can be regenerated using low-temperature waste heat, can also produce sufficient voltage for hydrogen gas generation in an MREC. The maximum hydrogen production rate was 1.6 m³ H₂/m³·d, with a hydrogen yield of 3.4 mol H₂/mol acetate at a salinity ratio of infinite. Energy recovery was 10% based on total energy applied with an energy efficiency of 22% based on the consumed energy in the reactor. The cathode overpotential was dependent on the catholyte (sodium bicarbonate) concentration, but not the salinity ratio, indicating high catholyte conductivity was essential for maximizing hydrogen production rates. The direction of the HC and LC flows (co- or counter-current) did not affect performance in terms of hydrogen gas volume, production rates, or stack voltages. These results show that the MREC can be successfully operated using ammonium bicarbonate salts that can be regenerated using conventional distillation technologies and waste heat making the MREC a useful method for hydrogen gas production from wastes