Figure 2. a) Contact angle measurements of CP and ACP. b) Contact angle measurements of CP/Ru and ACP/Ru. Snapshots of AIMD simulations for anchoring process of RuCl3 on c) pristine CP and d) ACP. Color codes: cyan (Ru), light green (Cl), red (O), white (H), and grey (C).
The crystal structures were analyzed by X-ray diffraction (XRD) (Figure 3 a). The XRD pattern exhibits two prominent peaks at approximately 26 and 54° which corresponds to the (002) and (211) planes of graphitic carbon, respectively. Due to the predominance of graphitic carbon peaks, the specific region of interest was magnified as presented in Figure 3b. Within this magnified region, both samples displayed a distinct peak at approximately 43°, indicating the presence of Ru (002) plane. Hydrogen temperature-programmed desorption (H2-TPD) was performed to investigate the kinetics of hydrogen adsorption and desorption on the electrode to understand the interaction between Ru atoms and hydrogen.[27] The lack of any peaks in the H2-TPD profile across the temperature range of 25 to 550 ℃ for the bare CP indicates its inherently inferior electrochemical characteristics, which will be further discussed in the following sections. Meanwhile, ACP/RuSAC+C shows H2 desorption starting at 300 ℃, with a prominent peak observed at around 500 ℃. This result aligns with previous research, where Ru-based catalysts typically exhibited desorption peaks within the temperature range of approximately 300 to 500 ℃ (Figure 3c).[28-31] To gain further insight into the existing form of Ru atoms in ACP/RuSAC+C, transmission electron microscopy (TEM) and aberration-corrected (AC) high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurements were conducted. Notably, these analyses revealed the presence of both Ru nanoclusters and a significant number of atomically distributed Ru atoms surrounding the nanoclusters (Figure 3d,e). Hence, we confirmed that the Ru atoms in ACP/RuSAC+C exist as both single atoms and nanoclusters. The lattice spacing of the Ru nanoclusters in ACP/RuSAC+C is ~0.216 nm, corresponding to the (002) plane of the Ru nanoclusters, which is in agreement with the XRD results. Moreover, statistical analysis, as presented in Figure 3f,g, demonstrates that the average distance between Ru single atoms and the closest nanoclusters is typically 4.24 ± 0.13 Å. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed uniform distributions of Ru, N, O, and C elements in the carbon matrix (Figure 3h).