Plasma is known as the "fourth state of matter", and as a special gas state substance, it is usually produced under high temperature or strong electromagnetic field. The composition of plasma includes ions, electrons, and non ionized neutral particles, which exhibit overall electrical neutrality. The existence form of plasma is very special because of its extremely high chemical activity and ability to interact with electromagnetic fields. This unique advantage makes it widely used in the field of surface strengthening of materials. Due to the presence of a large number of active particles such as activated molecules, activated atoms, electrons, photons, and free radicals in plasma, some chemical reactions with more stringent conditions can be more easily achieved.

The low-temperature plasma method has many advantages in modifying materials, such as environmental friendliness, convenient material processing, and no secondary pollution. Compared with hot plasma, low-temperature plasma has lower energy density and ionization degree. In low-temperature plasmas, electrons are more easily accelerated under the same electric field, and their temperature is usually much higher than that of ionized particles. Therefore, the plasma modification process is easily maintained at a lower temperature, even at room temperature. Therefore, the modification of adsorbent materials can be easily achieved using plasma technology, which is much more convenient than traditional chemical modification methods.

In order to enhance the bonding strength between carbon paper and catalyst materials, plasma treatment was used to modify the surface of carbon paper, and SEM, contact angle, and AFM analysis were performed on the treated carbon paper to explore the principle of enhancing the bonding strength between carbon paper and catalyst after plasma treatment.

Research on Plasma Modified Carbon Substrate Treatment

SEM analysis

From Figure 1 and Figure 2, it can be seen that after argon plasma treatment (300W, 5 minutes), the spherical particles on the surface of the carbon paper are bombarded and etched, without dendritic adhesion, with a more dispersed morphology and smaller particle size. Therefore, it is speculated that the area of catalyst that can be loaded on the carbon paper after plasma treatment is relatively increased.

SEM images of carbon paper before and after plasma treatment

Analysis of Contact Angle Testing

Measure the contact angle of carbon paper substrate with water using a contact angle tester, that is, the wettability of water on carbon paper. From Figures 3 and 4, it can be seen that after argon plasma treatment (300W, 5 minutes), the carbon paper substrate changed from hydrophobic (contact angle 154.7 °) to hydrophilic (contact angle 42.5 °), causing an increase in the binding force between the carbon substrate and water molecules, resulting in an increase in the binding force between the carbon paper substrate and metal ions in the electrodeposition solution. More catalyst clusters were deposited on a certain contact area, further improving the catalytic performance of the catalyst.

Comparison of Contact Angle before and after Plasma Treatment of Carbon Paper

AFM analysis

Using atomic force microscopy to investigate the physical properties, including morphology, of nanoscale carbon substrates. From Figures 5 and 6, it can be seen that compared to the untreated carbon substrate, the carbon substrate treated with Ar plasma is rougher, with dense peaks and valleys. From this, it can be inferred that plasma modification can change the surface roughness of materials through surface etching, which may eliminate weak boundaries on the surface of carbon paper substrates and introduce greater undulations on the carbon substrate surface, helping to increase the specific surface area and form more sites on the surface that can bind with catalysts and reactants.

AFM images of carbon paper before and after plasma treatment

After low-temperature plasma treatment, the physical properties of carbon paper change from hydrophobicity to hydrophilicity, and the surface roughness increases, with more peaks and valleys with certain height differences distributed on the surface. This indicates that argon plasma treatment of carbon paper substrate can enhance the interaction between the substrate and the catalyst, while expanding the contact area between the catalyst and reactants, thereby improving the overall reaction activity of the catalyst electrode material.