Nitrogen-doped graphene for catalysis

Nitrogen-doped graphene (N-Gr) has emerged as a transformative material in heterogeneous catalysis due to its tunable electronic properties and enhanced surface reactivity. Recent studies have demonstrated that the incorporation of nitrogen atoms into the graphene lattice significantly alters the charge distribution, creating active sites for catalytic processes. For instance, N-Gr exhibits a 2.5-fold increase in oxygen reduction reaction (ORR) activity compared to pristine graphene, with a half-wave potential of 0.85 V vs. RHE, rivaling platinum-based catalysts. Density functional theory (DFT) calculations reveal that pyridinic-N sites are particularly effective, lowering the activation energy barrier for ORR by 0.3 eV. These findings underscore the potential of N-Gr as a sustainable alternative to noble metal catalysts in fuel cells.

The catalytic performance of N-Gr in CO2 reduction reactions (CO2RR) has also garnered significant attention. Experimental results show that N-Gr achieves a Faradaic efficiency of 92% for CO production at -0.7 V vs. RHE, outperforming undoped graphene by 40%. The presence of graphitic-N sites enhances CO2 adsorption and stabilizes key intermediates, as confirmed by in-situ X-ray absorption spectroscopy (XAS). Additionally, N-Gr exhibits exceptional durability, maintaining 95% of its initial activity after 100 hours of continuous operation. These metrics position N-Gr as a promising candidate for large-scale CO2 conversion technologies.

In hydrogen evolution reactions (HER), N-Gr demonstrates remarkable efficiency due to its optimized hydrogen adsorption free energy (ΔGH*). Studies report that N-Gr achieves a current density of 10 mA/cm² at an overpotential of 120 mV, comparable to commercial Pt/C catalysts. The synergistic effect of pyridinic-N and graphitic-N sites reduces ΔGH* to -0.08 eV, close to the ideal value of zero. Furthermore, N-Gr exhibits excellent stability in acidic and alkaline media, with negligible performance degradation after 5000 cycles. These results highlight its potential for scalable hydrogen production.

N-Gr also excels in selective oxidation reactions, such as the conversion of alcohols to aldehydes. For example, benzyl alcohol oxidation using N-Gr yields benzaldehyde with a selectivity exceeding 98% and a turnover frequency (TOF) of 1200 h⁻¹ at 80°C. The high activity is attributed to the formation of reactive oxygen species at nitrogen defect sites, as evidenced by electron paramagnetic resonance (EPR) spectroscopy. Moreover, N-Gr can be easily separated and reused without significant loss in performance, making it an eco-friendly catalyst for fine chemical synthesis.

Finally, advancements in scalable synthesis methods have further bolstered the practical application of N-Gr in catalysis. Techniques such as chemical vapor deposition (CVD) and plasma treatment enable precise control over nitrogen doping levels and site distribution. Recent breakthroughs have achieved doping concentrations up to 12 at.% with uniform spatial distribution across large-area graphene sheets. This scalability ensures that N-Gr can meet industrial demands while maintaining its exceptional catalytic properties.

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