Electrified Ion Exchange Enabled by Water Dissociation in Bipolar Membranes for Nitrogen Recovery from Source-Separated Urine.
Environmental science & technology
Ion exchange (IX) is a promising technology for selective nitrogen recovery from urine; however, IX requires chemical-intensive regeneration that escalates energy consumption and carbon emissions. To overcome this barrier, we demonstrated and investigated a novel electrified IX stripping process (EXS) enabling electrochemical in situ IX regeneration with simultaneous ammonia stripping. EXS combines a weak acid cation exchange resin (WAC) to concentrate ammonia, a bipolar membrane to produce protons for WAC regeneration, and membrane stripping to recover the eluted ammonium from WAC. We observed over 80% regeneration (elution from resin) and recovery (membrane stripping) efficiencies during multiple adsorption-recovery cycles with synthetic and real urine. Comparing WAC with a strong acid cation exchange resin illustrated the critical role of the proton affinity of resin moieties in regulating resin regenerability and conductivity in EXS, which we distinguished from the rationale for material choice in electrodeionization. Compared to other electrochemical recovery methods using unamended wastewater as an electrolyte, EXS enabled control of electrolyte composition during recovery by separating and equalizing influent ammonium via WAC-mediated removal. This electrolyte engineering facilitated tunable EXS energy efficiency (100-300 MJ/kg N). This study informs the design of electrified, intensified systems that enable decentralized nitrogen recovery from urine.
View details for DOI 10.1021/acs.est.2c03771
View details for PubMedID 36223185
Probing dissolved CO2(aq) in aqueous solutions for CO2 electroreduction and storage.
2022; 8 (19): eabo0399
CO2 dissolved in aqueous solutions CO2(aq) is important to CO2 capture, storage, photo-/electroreduction in the fight against global warming and to CO2 analysis in drinks. Here, we developed microscale infrared (IR) spectroscopy for in situ dynamic quantitating CO2(aq). The quantized CO2(g) rotational state transitions were observed to quench for CO2(aq), accompanied by increased H2O IR absorption. An accurate CO2 molar extinction coefficient ε was derived for in situ CO2(aq) quantification up to 58 atm. We directly measured CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high-pressure conditions with high spectral and time resolutions. In KHCO3 electrolytes with CO2(aq) > ~1 M, CO2 electroreduction (CO2RR) to formate reached >98% Faradaic efficiencies on copper (Cu2O/Cu)-based electrocatalyst. Furthermore, CO2 dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO2(aq) supersaturation in aqueous systems, with implications to CO2 capture, storage, and supersaturation phenomena in natural water bodies.
View details for DOI 10.1126/sciadv.abo0399
View details for PubMedID 35559679
Catalytic Performance and Near-Surface X-ray Characterization of Titanium Hydride Electrodes for the Electrochemical Nitrate Reduction Reaction.
Journal of the American Chemical Society
The electrochemical nitrate reduction reaction (NO3RR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiHx, 0 < x ≤ 2). With ex situ grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH2 enrichment with increasing NO3RR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH2/Ti electrodes for use in NO3RR, thereby decoupling hydride formation from NO3RR performance. A wide range of NO3RR activity and selectivity on TiH2/Ti electrodes between -0.4 and -1.0 VRHE was observed and analyzed with density functional theory (DFT) calculations on TiH2(111). This work underscores the importance of relating NO3RR performance with near-surface electrode structure to advance catalyst design and operation.
View details for DOI 10.1021/jacs.2c01274
View details for PubMedID 35315649
Efficient CO2 electroreduction on facet-selective copper films with high conversion rate.
2021; 12 (1): 5745
Tuning the facet exposure of Cu could promote the multi-carbon (C2+) products formation in electrocatalytic CO2 reduction. Here we report the design and realization of a dynamic deposition-etch-bombardment method for Cu(100) facets control without using capping agents and polymer binders. The synthesized Cu(100)-rich films lead to a high Faradaic efficiency of 86.5% and a full-cell electricity conversion efficiency of 36.5% towards C2+products in a flow cell. By further scaling up the electrode into a 25 cm2 membrane electrode assembly system, the overall current can ramp up to 12A while achieving a single-pass yield of 13.2% for C2+ products. An insight into the influence of Cu facets exposure on intermediates is provided by in situ spectroscopic methods supported by theoretical calculations. The collected information will enable the precise design of CO2 reduction reactions to obtain desired products, a step towards future industrial CO2 refineries.
View details for DOI 10.1038/s41467-021-26053-w
View details for PubMedID 34593804
Selective aqueous ammonia sensors using electrochemical stripping and capacitive detection
View details for DOI 10.1002/aic.17465
Electroreduction of CO2 to Formate on a Copper-Based Electrocatalyst at High Pressures with High Energy Conversion Efficiency.
Journal of the American Chemical Society
Electrocatalytic CO2 reduction (CO2RR) to valuable fuels is a promising approach to mitigate energy and environmental problems, but controlling the reaction pathways and products remains challenging. Here a novel Cu2O nanoparticle film was synthesized by square-wave (SW) electrochemical redox cycling of high-purity Cu foils. The cathode afforded up to 98% Faradaic efficiency for electroreduction of CO2 to nearly pure formate under ≥45 atm CO2 in bicarbonate catholytes. When this cathode was paired with a newly developed NiFe hydroxide carbonate anode in KOH/borate anolyte, the resulting two-electrode high-pressure electrolysis cell achieved high energy conversion efficiencies of up to 55.8% stably for long-term formate production. While the high-pressure conditions drastically increased the solubility of CO2 to enhance CO2 reduction and suppress hydrogen evolution, the (111)-oriented Cu2O film was found to be important to afford nearly 100% CO2 reduction to formate. The results have implications for CO2 reduction to a single liquid product with high energy conversion efficiency.
View details for DOI 10.1021/jacs.0c00122
View details for PubMedID 32250611