Understanding interfaces’ functions and modifications in membrane electrode assembly of proton exchange membrane fuel cells

Interfaces in membrane electrode assembly (MEA) refer to the contacting region between two neighboring layers, and on both anodic and cathodic side, there are the proton exchange membrane/ catalyst layer...

Microbially Powered Electrochemical Systems Coupled with Membrane-based Technology for Sustainable Desalination and Efficient Wastewater Treatment

Objective:Seawater has a potential for managing the intensive potable drinking water demand. The recentconventional desalinating technologies are environmentally unsustainable and energy intensive. Thus, in the quest to find an alternative to the traditional desalination technologies, microbial desalination cells (MDC) have come into limelight. MDCs are considered the promising technologies for treating wastewater while simultaneously producing electricity, which can be utilized for desalinating seawater along with production of some value added products. However, some technical limitations associated with the practical usage of MDCs are pH maintenance at the cathodic side, internal resistance along with membrane fouling and its durability.Methods:These challenges can be dealt by utilizing various integrated configurations.Results and Discussion:Based on the study, the conventional technologies require less operational and maintenance cost but also less environmentally sustainable in comparison to these integrated MDC configurations.Conclusion:This review summarizes the basic working principles of MDCs, its types and factors affecting its performance and also several other applications associated with MDCs. This review also highlights various integrated MDC configurations which can be utilized for reducing the limitations associated to the conventional MDC system.

Treatment of Cyanide-Free Wastewater from Brass Electrodeposition with EDTA by Electrodialysis: Evaluation of Underlimiting and Overlimiting Operations

Growing environmental concerns have led to the development of cleaner processes, such as the substitution of cyanide in electroplating industries and changes in the treatment of wastewaters. Hence, we evaluated the treatment of cyanide-free wastewater from the brass electroplating industry with EDTA as a complexing agent by electrodialysis, aimed at recovering water and concentrated solutions for reuse. The electrodialysis tests were performed in underlimiting and overlimiting conditions. The results suggested that intense water dissociation occurred at the cathodic side of the commercial anion-exchange membrane (HDX) during the overlimiting test. Consequently, the pH reduction at this membrane may have led to the reaction of protons with complexes of EDTA-metals and insoluble species. This allowed the migration of free Cu2+ and Zn2+ to the cation-exchange membrane as a result of the intense electric field and electroconvection. These overlimiting phenomena accounted for the improvement of the percent extraction and percent concentration, since in the electrodialysis stack employed herein, the concentrate compartments of cationic and anionic species were connected to the same reservoir. Chronopotentiometric studies showed that electroconvective vortices minimized fouling/scaling at both membranes. The electrodialysis in the overlimiting condition seemed to be more advantageous due to water dissociation and electroconvection.

Dopant-tuned stabilization of intermediates promotes electrosynthesis of valuable C3 products

The upgrading of CO2/CO feedstocks to higher-value chemicals via energy-efficient electrochemical processes enables carbon utilization and renewable energy storage. Substantial progress has been made to improve performance at the cathodic side; whereas less progress has been made on improving anodic electro-oxidation reactions to generate value. Here we report the efficient electroproduction of value-added multi-carbon dimethyl carbonate (DMC) from CO and methanol via oxidative carbonylation. We find that, compared to pure palladium controls, boron-doped palladium (Pd-B) tunes the binding strength of intermediates along this reaction pathway and favors DMC formation. We implement this doping strategy and report the selective electrosynthesis of DMC experimentally. We achieve a DMC Faradaic efficiency of 83 ± 5%, fully a 3x increase in performance compared to the corresponding pure Pd electrocatalyst.

Influence of EDTA on the Electrochemical Removal of Mercury (II) in Soil from San Joaquín, Querétaro, México

<p>The removal of mercury from soil and Ca-bentonite was performed using electrochemical treatment adding ethylendiaminetetra acetic acid (EDTA) as a complexing agent to improve the electrochemical removal of Hg (II) in soil from San Joaquín, Querétaro, México. During the electrokinetic treatment in the presence of 0.1 M EDTA, most of Hg (II) migrates toward the anode obtaining the highest removal efficiencies close to 70 % in bentonite after 9 h. Using 0.1M HCl only 65 % efficiency was attained after 13 h in the cathodic side. EDTA formed a negatively charged stable complex that migrates to the cathode by the application of the electrokinetic treatment across Hg – EDTA synthesized complex.</p>

Tin electrodeposition from sulfate solution containing a benzimidazolone derivative

Tin electrodeposition in an acidic medium in the presence of N,N’-1,3-bis-[N-3-(6-deoxy-3-O-methylD-glucopyranose-6-yl)-2-oxobenzimidazol-1-yl)]-2-tetradecyloxypropane as an additive was investigated in this work. The adequate current density and the appropriate additive concentration were determined by gravimetric measurements. Chronopotentiometric curves showed that the presence of the additive caused an increase in the overpotential of tin reduction. The investigations by cyclic voltammetry technique revealed that, in the presence and in absence of the additive, there were two peaks, one in the cathodic side attributed to the reduction of Sn2+ and the other one in the anodic side assigned to the oxidation of tin previously formed during the cathodic scan. The surface morphology of the tin deposits was studied by scanning electron microscopy (SEM) and XRD.

Transient Analysis of Gas Distribution in the Anodic Flow Field in a Fuel Cell Stack

In a polymer electrolyte fuel cell (PEFC), the catalyst degradation on cathodic side is one of the fatal problems caused by mal-distributed hydrogen supply into each channel on active area in a fuel cell, especially in a fuel cell stack for automotive fuel cell systems which consist of several hundreds of fuel cells stacked. For example, before getting the fuel cell system started-up, the gas in all the anodic flow passage including channels in each fuel cell is occupied by air instead of hydrogen due to cross leak from cathodic side to anodic side through the membrane employed as an electrolyte. In this situation, if hydrogen is supplied partially or unevenly between cells to start up the system, a concentration interface of air and hydrogen will be made within a fuel cell. This causes a state of local cell within a single fuel cell and the catalyst degradation (carbon corrosion or Pt dissolution) occurs. In this paper, to avoid this catalyst degradation, the gas distribution is investigated with pressurized hydrogen supply into channels located on the hundreds stacked fuel cells statically filled with air initially. A transient computational fluid analysis was applied to the flow fields of anodic side which consist of channels on fuel cells, both distributing and collecting manifold connected to the fuel cells under parameters: 1) number of stacked fuel cells (i.e. manifold length), 2) the rate of pressure rising (Pa/sec.) which makes the gas flow velocity. A gas analysis experiment was also carried out for a validation with mass spectrometer taking gas sample from several points along the gas channels on alternative fuel cells which are made of transparent acrylic resin. The results show that the uniform distribution in concentration between cells and its profile within the channels along the flow direction are strongly affected by flow field formed within the distributing manifold located upstream of stacked plates with channels.

Experimental Study of Concentration Polarization at a Microchannel-Nanochannel Interface

Recent advances in fabrication methods allow us to study and leverage the unique flow regimes offered by nano-scale fluidic channels, [1–3] and recent work suggests that the physics of microchannel/nanochannel interfaces present opportunities for novel methods of sample preconcentration and analysis. [4–6] In nanochannels, channel height is of the same order of the electric double layer (EDL) thickness, leading to a decreased electrical resistance relative to the fluidic resistance of the channel. More importantly, analyte molecules undergoing electrophoresis spend a significant amount of time within EDLs. This has a profound effect on the interfaces between micro- and nanochannels. In particular, for negatively charged walls and a nanochannel in series with two microchannels, the concentration of ions (of both signs) increases on the cathodic side of the nanochannel and decreases on the anodic side. This phenomenon is called concentration polarization (CP) or the exclusion enrichment effect. [4, 5] There is a dearth of basic studies of these phenomena and the coupling of electroosmotic flow with concentration polarization. We present experimental validation of a computational model which predicts the development of concentration polarization. Furthermore, we will show preliminary results demonstrating focusing and separation of analyte anions in the cathodic side microchannel. This focusing is due to a balance of advection and electrophoretic migration. Anionic analytes focus and separate according to electrophoretic mobility.