L.G. Arriaga

Evaluation of single and stack membraneless enzymatic fuel cells based on ethanol in simulated body fluids

The purpose of this work is to evaluate single and double-cell membraneless microfluidic fuel cells (MMFCs) that operate in the presence of simulated body fluids SBF, human serum and blood enriched with ethanol as fuels. The study was performed using the alcohol dehydrogenase enzyme immobilised by covalent binding through an array composed of carbon Toray paper as support and a layer of poly(methylene blue)/tetrabutylammonium bromide/Nafion and glutaraldehyde (3D bioanode electrode). The single MMFC was tested in a hybrid microfluidic fuel cell using Pt/C as the cathode. A cell voltage of 1.035V and power density of 3.154mWcm-2 were observed, which is the highest performance reported to date. The stability and durability were tested through chronoamperometry and polarisation/performance curves obtained at different days, which demonstrated a slow decrease in the power density on day 10 (14%) and day 20 (26%). Additionally, the cell was tested for ethanol oxidation in simulated body fluid (SBF) with ionic composition similar to human blood plasma. Those tests resulted in 0.93V of cell voltage and a power density close to 1.237mWcm-2. The double cell MMFC (Stack) was tested using serum and human blood enriched with ethanol. The stack operated with blood in a serial connection showed an excellent cell performance (0.716mWcm-2), demonstrating the feasibility of employing human blood as energy source.

An electrokinetic-combined electrochemical study of the glucose electro-oxidation reaction: effect of gold surface energy

The glucose electro-oxidation reaction typically involves several steps and it is strongly influenced by the crystalline structure. In this paper, gold with typical {111} defects (namely Au{111}) and gold with defects enclosed in the (200) plane (Au{200}) were used to determine the effect of the surface energy in the adsorption and electro-oxidation of D-(+)-glucose. To this end, an electrokinetic analysis of surface species was made by means of zeta potential (ζ) measurements and was correlated with an electrochemical study. At low glucose concentration (0.1 mM), the system Au{200} showed a positive and large ζ value of 261.26 mV related to protons from the glucose dehydrogenation. Au{111} presented a negative ζ value of −98.11 mV associated to the glucose chemisorption plus OH− adsorption from the electrolyte. At a higher concentration (>20 mM) both systems exhibited positive ζ values (from 40 to 60 mV) related to the glucose dehydrogenation because of saturation of the electrical double layer by glucose molecules. Through cyclic voltammetry, it was observed that at low glucose concentration (<20 mM), both materials had preference for oxidation of glucose by-products. However, at higher concentrations, Au{111} favors glucono-lactone oxidation (0.4 V vs. NHE); meanwhile Au{200} favors glucose oxidation (−0.43 V vs. NHE). Through the electrokinetic analysis, the behavior of Au{111} can be related to its affinity toward the chemisorption of glucose molecules, and that of Au{200} to weak glucose chemisorption, which allows the desorption of glucose by-products renewing the gold surface for the further oxidation of glucose molecules.

Effect of metal content on the electrocatalytic activity of AuxPdy mixtures and their use in a glucose membraneless microfluidic fuel cell

AuxPdy bimetallic mixtures with different elemental contents were synthesized on glassy carbon electrodes using electrochemical techniques, which are easy, quick, versatile and cheap. Pulse potential and staircase techniques such as cyclic voltammetry (Au60Pd40), square-wave voltammetry (Au50Pd50 and Au35Pd65) and second harmonic AC voltammetry (Au15Pd85) were used to easily change the metal proportion and reduce the Au content in the AuxPdy mixtures. Au60Pd40 exhibited the most negative potential (−0.4 V vs. NHE) towards the glucose electro-oxidation reaction. For this reason, it was used in the anode compartment of a microfluidic fuel cell and compared with single Au and Pd materials by cyclic voltammetry. Au60Pd40 showed a greater negative potential than that of the Au anode; meanwhile, Pd showed no electrocatalytic activity. The lattice parameters were calculated by X-ray diffraction patterns resulting in values of 3.83 and 4.03 A for Au and Pd, respectively, and 3.94 A for Au60Pd40, which provides evidence for the internal structural changes due to the incorporation of Pd to the Au matrix. The maximum power density obtained with a glucose membraneless microfluidic fuel cell (GMMFC) using 10 mM glucose and Au60Pd40 as the anode was 0.28 mW cm−2.

Oxygen Reduction Reaction and PEM Fuel Cell Performance of a Chalcogenide Platinum Material

This work focuses on the development of electrocatalysts through a synthesis procedure with sulphur-platinum in combination with tungsten. We report a novel and simple synthetic method by chemical reaction using a thio-salt and metallic salts at room temperature. This chemical reaction produces a chemical electrocatalytic precursor which is thereafter supported in carbon Vulcan. After a thermal treatment at 400°C the electrocatalyst in the nanoscale length is obtained. In addition, commercial 20 wt.-% Pt/C (Electrochem) was used for comparison. The novel material was characterized electrochemically and by XRD and TEM before and after the thermal treatment. We investigated the effects of methanol toward the oxygen reduction reaction (ORR) on PtxWySz/C in 0.5M H2SO4 + 0.5M CH3OH. We measured a tolerance of ca. 80% in comparison to Pt/C. Fuel Cell measurements using two different assemblies (MEAs) were done by the hot-spray technique, the electrocatalytic inks were prepared and airbrush-deposited onto membrane.

Effect of pH in a Pd-based ethanol membraneless air breathing nanofluidic fuel cell with flow-through electrodes

In this work, a nanofluidic fuel cell (NFC) in which streams flow through electrodes was used to investigate the role of pH in the cell performance using ethanol as fuel and two Pd nanoparticles as electrocatalysts: one commercially available (Pd/C from ETEK) and other synthesized using ionic liquids (Pd/C IL). The cell performances for both electrocatalysts in acid/acid (anodic/cathodic) streams were of 18.05 and 9.55 mW cm-2 for Pd/C ETEK and Pd/C IL. In alkaline/alkaline streams, decrease to 15.94 mW cm-2 for Pd/C ETEK and increase to 15.37 mW cm-2 for Pd/C IL. In alkaline/acidic streams both electrocatalysts showed similar cell voltages (up to 1 V); meanwhile power densities were of 87.6 and 99.4 mW cm-2 for Pd/C ETEK and Pd/C IL. The raise in cell performance can be related to a decrease in activation losses, the combined used of alkaline and acidic streams and these high values compared with flow-over fuel cells can be related to the enhancement of the cathodic mass transport by using three dimensional porous electrodes and two sources of oxygen: from air and from a saturated solution.

Evaluation of alcohol dehydrogenase and aldehyde dehydrogenase enzymes as bi-enzymatic anodes in a membraneless ethanol microfluidic fuel cell

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AldH) enzymes were immobilized by covalent binding and used as the anode in a bi-enzymatic membraneless ethanol hybrid microfluidic fuel cell. The purpose of using both enzymes was to optimize the ethanol electro-oxidation reaction (EOR) by using ADH toward its direct oxidation and AldH for the oxidation of aldehydes as by-products of the EOR. For this reason, three enzymatic bioanode configurations were evaluated according with the location of enzymes: combined, vertical and horizontally separated. In the combined configuration, a current density of 16.3 mA cm-2, a voltage of 1.14 V and a power density of 7.02 mW cm-2 were obtained. When enzymes were separately placed in a horizontal and vertical position the ocp drops to 0.94 V and to 0.68 V, respectively. The current density also falls to values of 13.63 and 5.05 mA cm-2. The decrease of cell performance of bioanodes with separated enzymes compared with the combined bioanode was of 31.7% and 86.87% for the horizontal and the vertical array.

A bendable and compactdevice for low-power application

In this work we present a novelmodel of a membraneless microfluidic fuel celldevice based on adhesive polyester film fabricated by a non-sophisticated technique at room temperature and reached high performance. This concept overcomes the concerns about the reliability, versatility and weight of fuel cell devices for portable energy applications.Current densities until500 mA cm-2 and power densities about 90mW cm-2 were achieved using formic acid as fuel and air and dissolved oxygen as oxidant.

Highly Methanol Tolerant Cathode Based on PtAg for Use in Microfluidic Fuel Cell

In the present work, a methanol tolerant cathode catalyst was developed through the electrodeposition of bimetallic nanoparticles PtAg on a glassy carbon electrode using potentiostatic and voltammetric techniques. The resulting particles were characterized by Scanning Electron Microscopy (SEM) and electrochemical techniques. According to the SEM study the synthetized nanoparticles have semi-spherical shape and their average diameter is 100 nm. This material shows catalytic activity to the oxygen reduction reaction with high tolerance to methanol.

Laccase/AuAg Hybrid Glucose Microfludic Fuel Cell

In this work a hybrid microfluidic fuel cell was fabricated and evaluated with a AuAg/C bimetallic material for the anode and an enzymatic cathode. The cathodic catalyst was prepared adsorbing laccase and ABTS on Vulcan carbon (Lac-ABTS/C). This material was characterized by FTIR-ATR, the results shows the presence of absorption bands corresponding to the amide bounds. The electrochemical evaluation for the materials consisted in cyclic voltammetry (CV). The glucose electrooxidation reaction in AuAg/C occurs around − 0.3 V vs. NHE. Both electrocatalytic materials were placed in a microfluidic fuel cell. The fuel cell was fed with PBS pH 5 oxygen saturated solution in the cathodic compartment and 5 mM glucose + 0.3 M KOH in the anodic side. Several polarization curves were performed and the maximum power density obtained was 0.3 mWcm−2 .

A compact and bendable, hook-and-loop tape-based membraneless device for energy conversion

The new concept of a hook-and-loop tape-based membraneless device constructed on adhesive polyester film, which is fabricated using non-sophisticated and inexpensive fabrication techniques at room temperature, is presented. This concept overcomes the concerns about the reliability, versatility, weight, cost, lifetime and high performance of microfluidic fuel cell devices to satisfy the needs of portable energy applications. Current densities from 150 to 600 mA cm−2 and power densities from 40 to 132 mW cm−2 were achieved by varying the formic acid concentration, flow rates and by using air and dissolved oxygen as an oxidant.