This research focused on synthesis, characterization, and application of point-of-use catalytic reactive electrochemical membranes (REMs) for electrocatalytic NO reduction. Deposition of Pd-Cu and Pd-In catalysts to the REMs produced catalytic REMs (i.e., Pd-Cu/REM and Pd-In/REM) that were active for NO reduction. Optimal performance was achieved with a Pd-Cu/REM and upstream counter electrode, which reduced NO from 1.0 mM to below the EPAs regulatory MCL (700 μM) in a single pass through the REM (residence time ∼2 s), obtaining product selectivity of <2% toward NO/NH. Nitrate reduction was not affected by dissolved oxygen and carbonate species and only slightly decreased in a surface water sample due to Ca and Mg scaling. Energy consumption to treat surface water was 1.1 to 1.3 kWh mol for 1 mM NO concentrations, and decreased to 0.19 and 0.12 kWh mol for 10 and 100 mM NaNO solutions, respectively. Electrocatalytic reduction kinetics were shown to be an order of magnitude higher than catalytic NO reduction kinetics. Conversion of up to 67% of NO, with low NO (0.7-11 μM) and NH formation (<10 μM), and low energy consumption obtained in this study suggest that Pd-Cu/REMs are a promising technology for distributed water treatment.

Developing highly active oxygen evolution and reduction reaction (OER/ORR) bifunctional electrocatalysts is key to multiple technologies, including regenerative fuel cells and metal-air batteries. To this end, we have investigated structure–activity relationships in Pb2Ru2O7–x having pyrochlore structure by tuning the structural oxygen vacancy (Ovac) and metal oxidation states. Increase in Ovac with temperature boosts the ORR activity by facilitating molecular oxygen dissociation via decrease in work function. Ovac formation is accompanied by lowering of the Ru­(V)/Ru­(IV) ratio due to charge-compensation which leads to decreased OER activity. Air-annealing of Pb2Ru2O7–x accelerates the formation of Ovac in comparison to Ar-annealing since atmospheric oxygen facilitates the reduction and phase-segregation of Ru from Pb2Ru2O7–x as RuO2. A maximum bifunctionality index and specific bifunctionality index of 0.69 V and 274.0 μA/cm2 BET, respectively, are observed for pristine Pb2Ru2O7–x . However, the activity is skewed toward OER for pristine Pb2Ru2O7–x , creating an asymmetric bifunctional property which is not desirable for practical applications. To reduce the asymmetric behavior, pristine and air-annealed Pb2Ru2O7–x samples at 700 °C are physically mixed which yields a higher symmetric OER/ORR activity (|Δi OER(η = 0.25 V)‑ORR(η = −0.45 V) specific|: pristine = 0.25 mA/cm2 BET, Air-700 °C = 0.20 mA/cm2 BET, physical mixture = 0.037 mA/cm2 BET). The inverse OER/ORR relationship in Pb2Ru2O7–x is attributed to the presence of an optimal ratio of 0.75 for Ru­(V)/Ru­(IV) and Ovac/Olattice, which provides symmetric bifunctional activity essential in electrochemical devices. An increase in Ru­(V)/Ru­(IV) ratio in pristine Pb2Ru2O7–x with no detectable Ru dissolution in the electrolyte observed subsequent to a 5-h OER hold-test, confirming high stability.

Seawater electrolysis is emerging as one of the most promising technologies for hydrogen and oxygen generation for spatially constrained offshore and mobile-maritime applications. Herein, we show that lead ruthenate pyrochlore (Pb 2 Ru 2 O 7−x ) electrocatalyst displays higher OER (oxygen evolution reaction) activity and selectivity over parasitic ACSFR (active chlorine species formation reaction) in comparison to other reported electrocatalysts during simulated seawater electrolysis. The higher OER selectivity and activity of Pb 2 Ru 2 O 7−x as compared to benchmark RuO 2 is ascribed to the presence of a greater concentration of surface Ru(V) and oxygen vacancies. Simulated seawater electrolysis using Pb 2 Ru 2 O 7−x yields higher OER activity (60-fold) and selectivity at pH = 13 (∼99%) than at pH = 7 (∼68%) due to the unfavorable thermodynamics and kinetics of ACSFR at high pH. A current density of 275 mA/cm 2 is obtained at a cell voltage of 1.80 V at pH = 13 in an electrolyzer, with 10 mV voltage loss at 200 mA/cm 2 over 5 h of operation.

This research focused on improving mineralization rates during the advanced electrochemical oxidation treatment of agricultural water contaminants. For the first time, bismuth-doped tin oxide (BDTO) catalysts were deposited on Magneĺi phase (Ti n O 2n−1 , n = 4−6) reactive electrochemical membranes (REMs). Terephthalic acid (TA) was used as a OH • probe, whereas atrazine (ATZ) and clothianidin (CDN) were chosen as model agricultural water contaminants. The BDTO-deposited REMs (REM/BDTO) showed higher compound removal than the REM, due to enhanced OH • production. At 3.5 V/SHE, complete mineralization of TA, ATZ, and CDN was achieved for the REM/BDTO upon a single pass in the reactor (residence time ∼3.6 s). Energy consumption for REM/BDTO was as much as 31-fold lower than the REM, with minimal values per log removal of <0.53 kWh m −3 for TA (3.5 V/SHE), <0.42 kWh m −3 for ATZ (3.0 V/SHE), and 0.83 kWh m −3 for CDN (3.0 V/ SHE). Density functional theory simulations provided potential dependent activation energy profiles for ATZ, CDN, and various oxidation products. Efficient mass transfer and a reaction mechanism involving direct electron transfer and reaction with OH • were responsible for the rapid and complete mineralization of ATZ and CDN at very short residence times.

This study focuses on the development of electrochemical sensors for the detection of Ciprofloxacin (CFX) in natural waters and wastewater effluents. The sensors are prepared by depositing a layer of multiwalled carbon nanotubes (MWCNTs) dispersed in a porous Nafion film on to a boron-doped diamond (BDD) electrode substrate. The porous-Nafion-MWCNT/BDD electrode enhanced detection of CFX due to selective adsorption, which was accomplished by a combination of electrostatic attraction at -SO3(-) sites in the porous Nafion film and the formation of charge assisted hydrogen bonding between CFX and -COOH MWCNT surface functional groups. By contrast, the bare BDD electrode did not show any activity for CFX oxidation. The sensors were selective for CFX detection in the presence of other antibiotics (i.e., amoxicillin) and other nontarget water constituents (i.e., Cl(-), Ca(2+), humic acid, sodium dodecylbenzenesulfonate, salicylic acid, 4-aminobenzoic acid, and 4-hydroxybenzoic acid). A limit of detection of 5 nM (S/N = 5.04 ± 0.26) in a 0.1 M KH2PO4 supporting electrolyte (pH = 4.5) was obtained using differential pulse voltammetry. The linear dynamic ranges with respect to CFX concentration were 0.005-0.05 μM and 0.05-10 μM, and the sensitivities were 41 ± 5.2 μA μM(-1) and 2.1 ± 0.22 μA μM(-1), respectively. Sensor fouling was observed at high concentrations of some organic compounds such as 1 mM 4-aminobenzoic acid and 4-hydroxybenzoic acid. However, a short cathodic treatment fully restores sensor response. The results indicate that these sensors have application in detecting CFX in natural waters and wastewater effluents.

Cost-effective and highly active borohydride oxidation reaction (BOR) electrocatalysts are crucial for the advancement of direct borohydride fuel cells (DBFCs). Noble-metal electrocatalysts, such as Pd, are used as benchmark electrocatalysts because of their superior BOR activity. However, Pd suffers from catalyst poisoning because of strong binding with BH x intermediates at a high BOR overpotential, making it unsuitable for high DBFC performance, whereas Ni exhibits a low degree of catalyst poisoning because of a relatively weak binding of BH x intermediates. Density functional theory (DFT) calculations indicate a lowering of H-and OH-binding energies on bimetallic PdNi surfaces in comparison to their individual counterparts, thereby freeing more sites for BH 4 adsorption that is crucial for a high BOR rate. The as-synthesized bimetallic PdNi/C electrocatalyst exhibits higher current densities at a BH 4 concentration range of 50−500 mM than Pd/C and Ni/C. A DBFC unit with a pH-gradientenabled microscale bipolar interface employing PdNi/C, Pt/C, and H 2 O 2 as the anode, cathode, and oxidant, respectively, exhibits a power density of 466 ± 1.5 mW/cm 2 at 1.5 V, a peak power density of 630 ± 2 mW/cm 2 at 1.1 V, with an open-circuit voltage of 1.95 ± 0.01 V. Our bimetallic alloy electrocatalyst shows high DBFC performance, providing a pathway for the development of suitable BOR electrocatalysts.

NASA’s current mandate is to land humans on Mars by 2033. Here, we demonstrate an approach to produce ultrapure H2 and O2 from liquid-phase Martian regolithic brine at ∼−36 °C. Utilizing a Pb2Ru2O7−δ pyrochlore O2-evolution electrocatalyst and a Pt/C H2-evolution electrocatalyst, we demonstrate a brine electrolyzer with >25× the O2 production rate of the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) from NASA’s Mars 2020 mission for the same input power under Martian terrestrial conditions. Given the Phoenix lander’s observation of an active water cycle on Mars and the extensive presence of perchlorate salts that depress water’s freezing point to ∼−60 °C, our approach provides a unique pathway to life-support and fuel production for future human missions to Mars.

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