Understanding Nucleation and Growth Behavior of Electrodeposited Platinum Particles for Optimization of Metal-Insulator-Semiconductor Photoelectrodes
In order to fabricate well-defined, uniform MIS geometries the electrodeposition process must be finely tuned to control structure properties. Important to this goal is a deep understanding of the nucleation and growth behavior of the catalytic metal particles, and balancing the two processes through pulsed electrodeposition to control particle density and size. In order to nucleate on bare SiO2, a critical voltage or energy must be reached to electrodeposit platinum on the oxide surface. Once nucleated, particles deposited in this regime will continue to grow while additional particles are simultaneously nucleated nearby. By contrast, electrodeposition at a more positive potential will lead to preferential growth of existing particles rather than nucleation of additional particles.
To elucidate these regimes, two consecutive linear sweep voltammograms were performed in the electrodeposition electrolyte. As the scans sweep the potential more negative than E0[PtCl4]2-/Pt = 0.755 V, an onset potential for the reduction reaction/deposition can be seen. In Figure 2, the first scan in the electrodeposition solution reveals the potential required to nucleate Pt species onto bare SiO2 (1. nucleation), whereas the second scan defines a growth regime where Pt species preferentially reduce onto Pt particles (2. growth). Our goal is to nucleate then grow platinum nanoparticles to control density and size, respectively.
Figure 3 verifies this control over particle density/size through a two-step deposition. The controlled pulsed deposition (Fig 3a top) shows a lower density and smaller particle size than the deposition at a constant potential in the nucleation regime (Fig 3b bottom). Additionally, the electrode with the controlled deposition demonstrated an improved photoelectrochemical performance in comparison with the higher density electrode. This is a result of enhanced light absorption. Using this knowledge of nucleation and growth, we can create MIS photoelectrodes with optimal catalyst particle spacing, surface area, and optical properties for enhanced HER performance.
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