The demand for platinum has superseded the supply in catalytic applications such as in autocatalytic converters, fuel cells, the petroleum industry among others. This has resulted in platinum being an expensive industrial material and therefore, attempts have been made to fabricate platinum monolayer films and single-atom alloy catalysts. There have been reports on platinum monolayer deposition onto various nanoparticles and single-crystalline surfaces but little has been achieved in the fabrication of complete-monolayer platinum onto a large-piece three-dimensional bulk substrate having a complex geometry.
In a recent research published in Science Advances, Professor Shengzhong (Frank) Liu and coworkers developed an effective method for minimizing platinum usage by synthesizing platinum monolayers onto a large-surface-area three-dimensional nickel foam network by applying a buffer layer method. They have found out that the monolayer is similar to a thick platinum film for catalyzing the hydrogen evolution reaction but it is much much cheaper.
The authors observed that at a negative voltage, there was an increase in current density, which signified the completion of the deposition cycle. This then stabilized indicating the complete termination of the deposition. At zero voltage, the current density initially increased then dropped to zero which showed that there was an immediate desorption of the hydrogen layer to produce a fresh platinum surface.
From further analysis, there was a similar mass gain for every monolayer deposition cycle which meant that each platinum atom had a covalent radius similar to that of platinum. This proved that the coating process is based on the complete-monolayer mechanism. It was also evident that a hydrogen atom forms on top of a platinum atom and as such, the double layer protects the formed platinum surface from any further deposition hence a well-defined platinum monolayer coating is produced.
The researchers also noted that the platinum monolayer applied onto a metal nanofilm and nickel foam functions as a hydrogen evolution reaction catalyst in acidic condition, by lowering the onset potential, which is effective in water splitting. The reduction in overpotential causes increased catalytic activity in the hydrogen evolution reaction.
Further analysis showed that the platinum monolayer-coated catalyst attained catalytic activity that was as high as that of a thick platinum film. This shows that the platinum monolayer completely covered the nickel foam, which means that a complete-monolayer platinum coating is generated onto the large-surface area nickel foam substrate. It is therefore evident from the study that high-activity platinum catalyst can be fabricated with minimal platinum usage thereby minimizing its commercial application costs.
- Man Li, Qiang Ma, Wei Zi, Xiaojing Liu, Xuejie Zhu, Shengzhong Liu. Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction. Science Advances, 2015. Vol. 1, no. 8, e1400268
- Liuqing Pang, Yunxia Zhang, Shengzhong Liu, Monolayer-by-monolayer growth of platinum films on complex carbon fiber paper structure. Applied Surface Science 2017, 407, 386-390.
- Liuqing Pang, Man Li, Qiang Ma, Yunxia Zhang, Xianpei Ren, Doudou Zhang, Shengzhong Frank Liu, Controlled Pt Monolayer Fabrication on Complex Carbon Fiber Structures for Superior Catalytic Applications. Electrochim. Acta 2016, 222, 1522-1527.