Platinum is the most effective element for anodic methanol oxidation reaction (MOR) in direct methanol fuel cells. The electrocatalytic activity of Pt is highly dependent on its geometrical structure and the surrounding environment. To improve MOR activity and reduce Pt loading, conventional strategies have focused on tailoring the structure and/or morphology of Pt (e.g., by making hollow/framed or core-shelled Pt); and hybridizing Pt with other elements (e.g., Co, Ni, Sn, Bi, etc.). However, the Pt in these catalysts is usually assembled as a nanoparticle of diameter greater than 1 nm, leading to unsatisfactory mass activity. Furthermore, in MOR, Pt nanoparticles are susceptible to poisoning by adsorbed intermediates (COads), resulting in activity loss. Hence, developing new types of Pt-based MOR electrocatalysts with high activity and anti-poisoning capability is of both practical and fundamental significance. Single-atom catalysts (SACs) are emerging as a new class of catalysts with extraordinary activity towards many electrocatalytic reactions, including oxygen and hydrogen evolution, oxygen, CO2, and N2 reduction, and hydrogen and formic acid oxidation. Pt SACs have utmost utilization of Pt atoms and good capability for CO oxidation. However, the electrochemical dehydrogenation of methanol to CO in MOR requires at least three contiguous Pt atoms. Further, it has been reported that SACs consisting of Pt single atoms supported on carbon nanotubes are inactive towards MOR. Yet, we should note that these studies focused only on the Pt active centers rather than the entire catalysts, thereby neglecting the environment surrounding Pt. In this regard, enhancing the activity of single atomic Pt towards MOR is a scientifically significant and challenging topic. For SACs, the atomic coordination of single atoms also plays an important role in determining the catalytic activity. It has been shown that the electronic structure and coordination of the central single atoms can be adjusted by tuning the bonds between the single atoms and the substrate. Herein, we designed two types of Pt SACs. Thanks to a simple adsorption-impregnation preparation method, single Pt atoms were immobilized on RuO2 and carbon black (VXC-72) to obtain Pt1/RuO2 and Pt1/VXC-72, respectively. The Pt1/RuO2 SACs showed superb mass activity and stability towards the MOR, far superior to those of most Pt-based catalysts developed to date. The MOR mechanism including the dehydrogenation of methanol and CO electrooxidation is further studied by density functional theory (DFT), confirming the experimental observation that the prepared SACs are active for the alcohol oxidation reaction. This finding suggests an approach of SACs for direct alcohol fuel cells.

The introduction section provides a comprehensive literature review on the existing research on methanol oxidation reaction (MOR) catalysts. It highlights the limitations of conventional Pt-based catalysts, such as unsatisfactory mass activity and susceptibility to CO poisoning. The review then introduces single-atom catalysts (SACs) as a promising alternative, citing their success in other electrocatalytic reactions but noting the challenge of applying them to MOR due to the requirement of multiple Pt atoms for methanol dehydrogenation. The existing literature demonstrating the inactivity of Pt SACs on carbon supports is also discussed, setting the stage for the current research which aims to overcome this limitation by exploring the effect of the catalyst support.

The study employed a simple impregnation-adsorption method to synthesize atomically dispersed platinum on ruthenium oxide (Pt1/RuO2) and carbon black (Pt1/VXC-72). The method involved dispersing RuO2 or VXC-72 in distilled water, adding a H2PtCl6H2O solution dropwise, stirring at 70°C for 5 hours, filtering, washing, and drying. A control sample, Pt1/RuO2-H, was prepared by reducing Pt1/RuO2 in H2 at 80°C. Additionally, Pt1/RuO2-500 and Pt1/RuO2-700 were obtained by annealing Pt1/RuO2 in air at 500°C and 700°C respectively. The Pt content was measured using UV-vis spectroscopy. Catalyst characterization involved techniques such as Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and X-ray Absorption Fine Structure (XAFS) spectroscopy to analyze the morphology, structure, coordination environment, and electronic configuration of the synthesized catalysts. HAADF-STEM and EDS mapping were used to visualize the atomic distribution of Pt on the supports. The oxidation states of Pt were determined using XANES analysis, and coordination numbers were obtained from EXAFS fitting. Electrochemical characterization employed cyclic voltammetry (CV) in a three-electrode setup using a N2-saturated 0.1 mol L-1 KOH and 1 mol L-1 methanol solution to evaluate the MOR performance of the catalysts. The mass activity was calculated, and CO stripping tests were conducted to assess CO tolerance. Chronoamperometry was used to evaluate the long-term durability. Finally, density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP) to study the MOR mechanism and determine the reaction free energies and energy barriers for methanol oxidation to CO on different models (Pt-RuO2(110), PtC3, Pt-Ru(0001)). Bader charge analysis and projected density of states (PDOS) calculations were conducted to investigate the electronic structure and charge distribution.

The key findings of the study demonstrate the superior performance of the Pt1/RuO2 single-atom catalyst for methanol oxidation reaction (MOR) in alkaline media. Specifically: 1. **High Mass Activity:** Pt1/RuO2 exhibited a mass activity of 6766 mA mgPt-1 at 0.80 V vs. RHE, which is 15.3 times higher than that of commercial Pt/C (441 mA mgPt-1 at 0.92 V vs. RHE). This surpasses the activity of most previously reported Pt-based catalysts. 2. **Enhanced CO Tolerance:** Pt1/RuO2 displayed a significantly higher peak current ratio (If/Ib) of 3.67 compared to Pt/C (1.81), indicating improved resistance to CO poisoning, a major limitation in MOR catalysts. 3. **Excellent Stability:** The Pt1/RuO2 catalyst maintained 95.5% of its initial mass activity after 10 hours of chronoamperometry, demonstrating remarkable stability. 4. **Atomic Dispersion:** HAADF-STEM images confirmed the atomic dispersion of Pt atoms on the RuO2 support, with no Pt clusters or nanoparticles observed. 5. **Influence of Pt Coordination:** The study showed a clear relationship between the coordination environment of Pt atoms and catalytic activity. Pt1/RuO2 (Pt-O coordination) was highly active, while Pt1/VXC-72 (Pt-C coordination) and Pt1/RuO2-H (Pt-Ru coordination) were essentially inactive, highlighting the critical role of the RuO2 support and the specific Pt-O3-Rucus-Obr configuration. 6. **DFT Simulations:** DFT calculations corroborated the experimental findings, indicating that the Pt-O3-Rucus-Obr bonds in Pt1/RuO2 facilitate electrochemical dehydrogenation of methanol with lower energy barriers and onset potential compared to Pt-C and Pt-Ru bonds. The calculations also supported the enhanced CO electrooxidation on Pt1/RuO2, explaining the superior CO tolerance observed experimentally. The calculations showed that the dehydrogenation of CH2O* was the rate-limiting step, and that Pt single atom incorporation lowered the activation energy barrier for this step. 7. **Ethanol Oxidation:** The Pt1/RuO2 catalyst also showed a significantly higher mass activity for ethanol oxidation reaction (EOR) in alkaline media, suggesting its potential for broader applications in alcohol oxidation reactions.

The superior performance of the Pt1/RuO2 single-atom catalyst can be attributed to two main factors: the high number of atomic Pt active sites and the unique coordination environment provided by the RuO2 support. The DFT calculations reveal that the presence of Pt-O3 (3-fold coordinatively bonded oxygen) - Rucus (coordinatively unsaturated Ru) bonds with undercoordinated bridging O (Obr) in Pt1/RuO2 lowers the energy barriers and onset potential for the electrochemical dehydrogenation of methanol, explaining the enhanced activity. The presence of RuO2 also enhances the CO electrooxidation process, significantly improving CO tolerance and catalyst stability. This synergistic effect between the Pt single atoms and RuO2 support is crucial for achieving the high performance observed in this study. The finding that Pt-C and Pt-Ru coordination environments are inactive emphasizes that tailoring the coordination of single atoms is essential for maximizing electrocatalytic activity. The high mass activity and stability of Pt1/RuO2 offer a promising approach for developing high-performance catalysts for MOR and other alcohol oxidation reactions. This work significantly advances the understanding of SACs and their potential for practical applications in fuel cells.

This research successfully synthesized a highly efficient single-atom catalyst (Pt1/RuO2) for methanol oxidation, exhibiting significantly enhanced mass activity and CO tolerance compared to commercial Pt/C. The superior performance is attributed to the unique Pt-O3-Rucus-Obr coordination environment in Pt1/RuO2, which facilitates methanol dehydrogenation and CO electrooxidation as confirmed by DFT calculations. This study provides valuable insights into designing high-performance single-atom catalysts for MOR and related alcohol oxidation reactions. Future research could explore other supports and single-atom metals to further optimize catalyst performance and investigate the scalability and applicability of these catalysts in practical fuel cell systems.

While this study demonstrates the remarkable catalytic activity and stability of Pt1/RuO2 for MOR, there are some limitations. The synthesis method, while simple, may require optimization for large-scale production. Further research is needed to investigate the long-term stability under more demanding operating conditions, such as higher temperatures and different fuel concentrations. The DFT calculations rely on specific models and approximations, and experimental verification of the proposed reaction mechanism could strengthen the conclusions. Finally, the study focuses primarily on alkaline media; exploring the performance in acidic media would broaden the applicability of this catalyst.