Researchers have realised an 11 times increase in a fuel cell’s oxygen reduction reaction by adding caffeine to the electrodes.
According to the team from Chiba University, Japan, the addition of caffeine can enhance the efficiency of the fuel cell, reduce the requirement for excess platinum catalysts, and lead to cheaper and more efficient fuel cells.
In a hydrogen fuel cell, hydrogen undergoes oxidation at the anode, producing hydrogen ions and electrons. The ions move through the electrolyte to the cathode, and electrons flow through an external circuit, generating electricity. At the cathode, oxygen combines with the hydrogen ions and electrons, resulting in water as a by-product.
The water reacts with the platinum (Pt) catalyst, forming a layer of platinum hydroxide (PtOH) on the electrode, which obstructs the efficient catalysis of the oxygen reduction reaction (ORR), leading to energy losses. To maintain efficient operation, fuel cells require a high Pt loading, which increases the costs of fuel cells.
Now, in a study published in Communications Chemistry, Professor Nagahiro Hoshi, along with Masashi Nakamura, Ryuta Kubo, and Rui Suzuki have found that adding caffeine to certain platinum electrodes can increase the activity of the ORR.
“Caffeine, one of the chemicals contained in coffee, enhances the activity of a fuel cell reaction 11-fold on a well-defined Pt electrode of which atomic arrangement has a hexagonal structure,” Professor Hoshi said in a statement.
To assess caffeine’s impact on the ORR, researchers measured current flow through platinum electrodes immersed in an electrolyte containing caffeine.
According to the team, these platinum electrodes had surface atoms arranged in specific directions, namely (111), (110), and (100).
There was said to be a notable improvement in the electrode’s ORR activity with an increase in caffeine concentration in the electrolyte. Caffeine, when present, adsorbs onto the electrode’s surface, preventing hydrogen adsorption and the formation of Pt oxide on the electrode. However, the effect of the caffeine depended on the orientation of the platinum atoms on the electrode’s surface.
At a caffeine molar concentration of 1 × 10−6, the ORR activity on Pt(111) and Pt(110) increased by 11 and 2.5 times, respectively, with no noticeable effect on Pt(100).
To understand this difference, the researchers investigated the molecular orientation of caffeine on the electrode surface using Infrared Reflection Absorption Spectroscopy.
They found that caffeine gets absorbed on Pt(111) and Pt(110) surfaces with its molecular plane perpendicular to the surface. However, on Pt(100), steric hindrances cause it to be attached with its molecular plane tilted relative to the surface of the electrode.
“The increased ORR activity of Pt(111) and Pt(110) was attributed to the decreased PtOH coverage and lower steric hindrance of the adsorbed caffeine. Conversely, for Pt(100), the effect of decreasing PtOH was counteracted by the steric hindrance of the adsorbed caffeine, and thus caffeine did not affect the ORR activity,” said Prof. Hoshi.
