An Electrodeposited Pd-Co Cathode Catalyst for a Microfabricated Direct Methanol Fuel Cell

Abstract

Pd-Co was electrodeposited as a rough cathode catalyst for a direct methanol fuel cell fabricated using micro-electromechanical systems technology. Pd-Co was electrodeposited at -10 mA/cm2 for 60 s or -200 mA/cm2 for 5 s. The deposits were evaluated with respect to microstructures, electrochemical characteristics, and fuel cell performances. As a result, oxygen reduction activity of the sample prepared at -200 mA/cm2 was higher than that prepared at -10 mA/cm2, while the electrochemically active surface areas were almost the same. Microstructures of the former and the latter were observed dendritic and flat, respectively. We conclude that the difference of oxygen reduction activity is attributed to the difference of the microstructure. In addition, we modified the dendritic sample by depositing Pd-Co at -0.75 V vs. Ag/AgCl. The modification increased open circuit potential for oxygen reduction by 30 mV from 0.70 to 0.73 V.

Prospects of on-chip fuelcell performance: improvement based on numerical simulation

“…Likewise, for the Pd-Co catalyst, the exchange current density based on geometrical area was determined to be 4.85 Â 10 À7 A m À2 . By comparing the performance with our previous papers, 18,19 since the performance of this catalyst was confirmed to be typical for Pd-Co catalyst, the value is confirmed to be valid. The value is for the oxygen-saturated solution, hence we used 0.97 Â 10 À7 A m À2 as the exchange current density for the air-saturated solution (p ¼ 0.2).…”

“…Since the cell was a membraneless design, one may be concerned that the methanol oxidation reaction occurs on the cathode, but it is assumed to be negligible because of the use of a selective catalyst, i.e., Pd-Co alloy. 18,19 In addition, it is assumed that oxygen reaction at the anode is negligible, because both the diffusivity and the solubility of oxygen in aqueous solutions are low.…”

“…60 mV decade À1 ). 18,19 Thus, the drastic decrease above 4 mA is attributed to the mass-transfer limitation, i.e., to slow oxygen diffusion. That is, cell performance was limited mainly by slow oxygen transport to the cathode.…”

Mesoporous PdCo sponge-like nanostructure synthesized by electrodeposition and dealloying for oxygen reduction reaction

“…We have not appreciated the fairly smaller value so far, but the favorably small Tafel slope seemed typical for electrodeposited PdCo catalyst and dealloyed PdCo catalyst. 29,36 Considering the fact that the slopes of PdCo synthesized by other methods were reported to be in the range of 60-70 mV s À1 , 16,37,38 the unique slope of our PdCo is of fundamental interest and of significant importance.…”

On-chip fuel cells for safe and high-power operation: investigation of alcohol fuel solutions

“…Third, a monolithic design is of great importance as we previously described. This unique design was realized by (i) the synthesis of a Pd-Co alloy, which was highly active in oxygen reduction reaction and tolerant to methanol, 15,16 using electrodeposition, 17,18 and (ii) the precise fabrication of microelectrodes with a narrow distance between them using microfabrication techniques. Previously, the cell had been demonstrated to operate on a methanol solution containing sulfuric acid or sodium sulfate as the supporting electrolyte, 6 which was necessary for the smooth ion-transfer between the anode and the cathode (Fig.…”