Voltage Inversion Caused by Self-organized Oscillations in a Direct Formic Acid Fuel Cell

Nogueira, Jéssica Alves; Varela, Hamilton

doi:10.19185/matters.201705000005

Cited by 4 publications

(9 citation statements)

References 18 publications

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“…[22] In addition, in 2017, we raised the possibility that the slow kinetic of oxygen reduction reaction, although it may not be the origin of such oscillatory behavior, plays a role on the voltage inversion during the operation of a DFAFC. [24] Herein, we deepen the understanding of the dynamics in these devices and show experimentally that the cathodic potential is sensitive to what is happening at the anode. By using a salt bridge approach, we were able to follow how the anodic or the cathodic overpotential evolve during a linear sweep voltammetry, galvanodynamic sweep and chronopotentiometry of fuel cells fed directly with methanol (DMFC, Direct Methanol Fuel Cell) or formic acid (DFAFC, Direct Formic Acid Fuel Cell).…”

Section: Introductionmentioning

confidence: 97%

“…[9,10,11,12,13,14,15,16,[17][18] There are various studies on how autonomous oscillatory behavior occurs in fuel cells based on the electro-oxidation of H 2 /CO [19,20,21] and, recently, methanol [22] and formic acid. [23,24] We should point out that, hitherto, all reports of oscillatory dynamics in fuel cells have been attributed to anodic processes. However, since the cathodic and anodic reactions take place at the same time and are coupled through the electric potential and chemical species, an important question that we will try to answer in this work is: Is the cathode affected by the self-organization on the anode?…”

Section: Introductionmentioning

confidence: 99%

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Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

2019

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An external reference electrode was used to monitor individually the evolution of the anodic and cathodic potentials during the stationary as well as oscillatory operation of a Direct Formic Acid Fuel Cell (DFAFC) and a Direct Methanol Fuel Cell (DMFC). Besides evidencing the large activation loss in both cells, we were able to observe how the oscillatory operation of such devices affects their cathodes. In fact, cathodic oscillations synchronized with the cell voltage dynamics were observed, hitherto never reported on fuel cells. We have addressed these phenomena taking into account two main coupling processes: through the proton concentration and a global coupling stemming from the control mode (potentiostatic or galvanostatic).

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

2019

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“…Formic acid is one of the most valuable CO 2 RR products, since it can be used as a building block for fine chemicals . Moreover, formic acid can be used in low‐temperature direct fuel cells, with higher efficiency than other C1 and C2 liquid alcohol fuels . In this context, it is still necessary to develop catalysts with onset potential and current densities optimized for CO 2 RR.…”

Section: Introductionmentioning

confidence: 99%

Effect of Annealing Treatment on Electrocatalytic Properties of Copper Electrodes toward Enhanced CO₂ Reduction

Lopes

Varela

2018

ChemistrySelect

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CO2 reduction (CO2RR) into added‐value chemicals is a key contribution to solve energetic and environmental issues. The performance of Cu‐based electrodes towards CO2RR is strongly affected by pretreatments and presence of impurities, such as copper oxides. We evaluated the effect of different treatments, electropolishing (Cu‐p), and annealing treatments under oxidizing (Cu‐Air) and reducing (Cu‐H2) conditions, on the performance of Cu electrodes designed for CO2RR. Characterizations revealed the presence of Cu2O and CuO layers on the surface of the Cu‐Air electrode. All electrodes formed only HCOO− ions as liquid‐phase products, with yield of 480 mg L−1 of HCOO− and Faradaic efficiency (FE) of 30% for the Cu‐Air electrode and 25 mg L−1 with FE of 16%, and 26 mg L−1 with FE of 10% for the Cu‐p and Cu‐H2 electrodes, respectively. Overall, the HCOO− concentration increased with an increasing KHCO3 concentration, while the FE increased up to 46%, due to insertion of CO2 into the electrical double layer, generating an intermediate specie prior to the electrochemical CO2RR. CO2RR tests performed on the Cu‐Air and Cu‐p electrodes under galvanostatic conditions showed HCOO− FE of 32% and 16%, respectively. Therefore, the increasing local pH mechanism does not play a key role in the liquid‐phase products of CO2RR. The activity of the Cu‐Air electrode for CO2RR remained stable over 64 hours. It was proposed that Cu1+ was the active site responsible for CO2RR. CO, C2H4, C2H6 and H2 were formed by gas‐phase electrochemical CO2RR using the Cu‐Air electrode, with total FE higher than 65%. We have uncovered the role played by the type of pre‐treatment in the performance of Cu‐based electrodes on CO2RR and the reason for the increased electrocatalytic activity of oxidized Cu electrodes.

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“…88 Based on the presented results, one can note the ubiquity of a catalytic poison, usually COad, underling the emergence of oscillatory kinetics during the electro-oxidation of small organic molecules. 12,13,18,19,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] This is the case for DMFC, DFAFC, and DEFC, with the latter still having the participation of CH3COOad that reverberates the effect of COad. 39 Although there are no reports of oscillatory kinetics during DME electro-oxidation, the steps described between r17 to r23, lead us to assume that such dynamic is in principle possible in DDMEFC.…”

Section: Direct Dimethyl Ether Fuel Cellmentioning

confidence: 99%

“…Except for the latter, there are several studies on potential and/or current oscillations during the electro-oxidation of small organic molecules in half-cell experiments, 12,13,[27][28][29][30][31][32][33][34][35][36][37][38][39] but studies in practical systems are still scarce. Also, of the few that exist, 17,19,[40][41][42] none is dedicated to exploring the effect of temperature on cell dynamics, although this is a fundamental bifurcation parameter in the oscillations observed in the PEMFC anode. 43…”

Section: Introductionmentioning

confidence: 99%

Direct Liquid Fuel Cells – The Influence of Temperature and Dynamic Instabilities

Nogueira¹,

Varela²

2020

Preprint

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The interconversion between chemical and electrical energies plays a pivotal role in the challenge for a sustainable future. Proton exchange membrane (PEMFC) based on the electro-oxidation of hydrogen and reduction of oxygen comprise a relatively mature technology of indisputable relevance. Alternatively, some open questions concerning the use of Direct Liquid Fuel Cells (DLFC) call for further experimental investigations on these systems. In this paper we evaluate the temperature effect on DLFCs under conventional and oscillatory conditions. We studied four molecules: methanol, formic acid, ethanol, and dimethyl ether. The use of identical experimental conditions allowed at studying the role of the fuel on the DLFC performance, providing thus reference values for future investigations. Under regular, non-oscillatory regime, we observed for all cases that the overpotential decreases as the temperature increases mainly because water activation on the catalyst surface is facilitated at high temperatures. By mapping the conditions where oscillatory kinetics manifest itself under galvanostatic mode, only the electro-oxidation of dimethyl ether did not exhibit potential oscillations. The relationship between oscillatory frequency and temperature during the methanol and formic acid electro-oxidation followed a conventional Arrhenius dependence, whereas with ethanol there was no straightforward trend, and temperature compensation prevails. The atypical behavior found for ethanol was addressed in terms of its main electrocatalytic poisons: adsorbed CO and acetate. The absence of oscillations during dimethyl ether electro-oxidation was attributed to its weak interaction with the catalyst surface.<br>

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Voltage Inversion Caused by Self-organized Oscillations in a Direct Formic Acid Fuel Cell

Cited by 4 publications

References 18 publications

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

Effect of Annealing Treatment on Electrocatalytic Properties of Copper Electrodes toward Enhanced CO₂ Reduction

Direct Liquid Fuel Cells – The Influence of Temperature and Dynamic Instabilities

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Voltage Inversion Caused by Self-organized Oscillations in a Direct Formic Acid Fuel Cell

Cited by 4 publications

References 18 publications

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

Effect of Annealing Treatment on Electrocatalytic Properties of Copper Electrodes toward Enhanced CO2 Reduction

Direct Liquid Fuel Cells – The Influence of Temperature and Dynamic Instabilities

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Product

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Effect of Annealing Treatment on Electrocatalytic Properties of Copper Electrodes toward Enhanced CO₂ Reduction