Electrocatalytic Reduction of Nitrate Using Magnéli Phase TiO₂ Reactive Electrochemical Membranes Doped with Pd-Based Catalysts

Abstract

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.

Janus electrocatalytic flow-through membrane enables highly selective singlet oxygen production

“…Spatial confinement by membrane pores and channels allows for optimal utilization of electrons by reactants due to minimal diffusion distance and mass transfer enhancement 30,32 , thereby overcoming intensive chemical usage in conventional EC systems. In addition, studies also highlighted the importance of flowthrough configuration of membrane electrodes, which renders electrons to flow parallel to the fluid flow direction, further enhancing the charge transfer rates compared to the conventional flow-by mode (i.e., when the flow direction and electric field direction are perpendiculars) 33,34 . To date, reported electrocatalytic membranes render only half-cell reaction (cathodic reduction or anodic oxidation) within a membrane substrate.…”

Membrane processes

“…Another research team developed a catalytic reactive electrochemical membrane (REM) for nitrate reduction (Gayen, Spataro, et al, 2018). This treatment system was considered competitive with RO for point of use treatment systems.…”

Alloying effect-induced electron polarization drives nitrate reduction to ammonia

“…32 However, they did not discuss whether this promotion effect is feasible. By comparing the differences in other applications of NiCu and PdCu alloys, [15][16] such promotion effect should be more obvious for PdCu alloys in NITRR. PdCu alloys are therefore chosen to study reaction mechanism on how the change of adsorption sites of Cu alloys affects the intermediates in NITRR, which has not been unveiled.…”

“…[1][2][3] Therefore, greater demand for NH3 is foreseeable. [4][5] The industrial NH3 synthesis through the classical Haber-Bosch process demands drastic reaction conditions of high pressures (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) and temperatures (300-550 o C), 6 which consumes 1-2% of the world's annual energy supply. [7][8][9] Considering such extremely harsh condition and fossil fuels shortage, NH3 production at atmospheric pressure and under ambient temperature is one of the greatest challenges and has been pursued actively for over a century.…”

“…14 Among all the nitrogencontaining alternatives, nitrate (NO3 -) is undoubtedly the most promising. [15][16] The disintegration of NO3into the deoxygenated species only requires an energy of 204 kJ/mol, much lower than the cleavage energy of N≡N bond (941 kJ/mol). [13][14] Meanwhile, higher reaction energy barrier for N2 reduction occurring at solid-gas-liquid interfaces is demanded compared to that of nitrate reduction reaction (NITRR) at solid-liquid interfaces.…”