Nitrogen-doped graphene quantum dots anchored on NiFe layered double-hydroxide nanosheets catalyze the oxygen evolution reaction

The design and synthesis of efficient, durable, low-cost catalysts are vital for the oxygen evolution reaction (OER) because it is an important process in energy conversion and storage. Here, we describe the use of a simple hydrothermal process to successfully synthesize novel nitrogen-doped graphene quantum dots (N-GQDs) anchored on NiFe layered double hydroxide sheets (N-GQDs/NiFe-LDH). Structural, morphological, and crystalline phase characteristics were confirmed by applying SEM, TEM, XPS, and XRD studies. These analyses clearly showed the formation of the N-GQDs/NiFe-LDH composite with a hierarchical nanosheet structure possessing higher surface area values and a wide range of pores (10-180 nm). Further study showed that the as-prepared N-GQDs/NiFe-LDH composite exhibited excellent electrocatalytic activity for the OER in alkaline solution, affording small overpotential of 279 and 300 mV at current densities of 20 and 50 mA cm(-2), respectively, a low Tafel slope of 47 mV dec(-1), and satisfactory stability. The outstanding reactive kinetics outperformed those of most previously reported transition-metal-based catalysts. The excellent OER catalytic activity for the N-GQDs/NiFe-LDH composite is attributed to the synergistic effect of the N-GQDs and NiFe-LDH, the existence of pyridinic-N and graphitic-N on the N-GQDs, and the hierarchical nanosheet and its porous structure. This work provides a new strategy for designing and fabricating novel carbon-based LDH composites.