Nitrogen-doped hollow carbon spheres as highly effective multifunctional electrocatalysts for fuel cells, Zn air batteries, and water-splitting electrolyzers

Clean energy conversion technologies require low-cost multifunctional catalysts. In this work, nitrogen-doped hollow carbon spheres with nanoporous shells (NHCS-W) are prepared by using the ionic liquid 1-butyl-3-methylimidazolium chloride as a source of both carbon and nitrogen. A systematic investigation of the electrocatalytic performance and durability of NHCS-W reveals excellent performance and high stabilities for the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline electrolytes. This multifunctionality facilitates promising practical applicability for NHCS-W. An alkaline exchange membrane fuel cell (AEMFC) with NHCS-W as the cathode electrocatalyst has a peak power density of 109 mW cm(-2), which is 7 mW cm(-2) higher than that of an AEMFC with Pt/C (20%) as the cathode electrocatalyst. By using NHCS-W as an air electrode, two rechargeable Zn-air batteries in series can power a 5 mm red light-emitting diode (similar to 2.2 V). Moreover, a cell voltage of only 1.61 V is needed to achieve a current density of 10 mA cm(-2) in a water-splitting electrolyzer employing NHCS-W as both the cathode and anode catalysts. This work reveals the potential of ionic liquid precursors for constructing nitrogen-doped carbon-based materials for a wide variety of electrocatalytic applications.