Boosting oxygen reduction catalysis with abundant copper single atom active sites

With their high catalytic activity, stability, selectivity, and 100% atom utilization, single atomic non-noble metal based materials are valuable alternatives to efficient but expensive Pt based catalysts. For efficient catalysis, single-atom catalysts must expose abundant single atomic metal active centers. Here, we report the rational design and synthesis of a Cu single-atom catalyst with high Cu content of over 20.9 wt%, made of single atomic Cu anchored into an ultrathin nitrogenated two-dimensional carbon matrix (Cu-N-C). The high Cu content was achieved by the introduction of additional N species, which can securely trap and protect the Cu atoms. During oxygen reduction, the single atomic Cu exhibited over 54 times higher mass activity than metallic Cu nanoparticles at a potential of 0.85 V versus a reversible hydrogen electrode (RHE). Furthermore, the Cu-N-C exhibited 3.2 times higher kinetic current at 0.85 V (vs. RHE), and a much lower Tafel slope (37 mV dec(-1)), as well as better methanol/carbon monoxide tolerance and long-term stability than commercial Pt/C. Density functional theory (DFT) calculations reveal that the Cu active sites exhibit improved O-O bond stretching and favorable adsorption energies of O-2 and OOH for four-electron oxygen reduction.