Hexagonal Boron Nitride-Supported Crystalline Manganese Oxide Nanorods/Carbon: A Tunable Nanocomposite Catalyst for Dioxygen Electroreduction

Dioxygen reduction is a key step in low-temperature fuel cell catalysis research and ultimately of sustainable energy conversion technology. Herein, we report a simple strategy to design a cost-effective electrocatalyst comprising MnO2 nanorods on hexagonal boron nitride (h-BN) and their composite with high surface area carbon by a chemical method. The optimized nanocomposite catalyst (MnBN/C-75) exhibits a substantial higher onset potential (E-onset = 0.9 V vs RHE) and limiting kinetic current density (J(L) = 5.6 mA cm(-2)) during the oxygen reduction reaction (ORR) compared to other reported h-BN-based metal-supported or metal-free electrocatalysts. Moreover, this catalyst shows a similar to 4-electron transfer pathway with a low peroxide (HO2-) intermediate yield during electroreduction of oxygen, indicating a single step, first order kinetics as a commercial Pt/C catalyst. Besides, the mass activity of 222 mA mg(-1) calculated at 0.6 V for the MnBN/C-75 catalyst is similar to 21 times higher than that of MnBN (10.4 mA mg(-1)) and slightly lower than Pt/C (239 mA mg(-1) at 0.9 V). Importantly, the MnBN/C-75 nanocomposite reveals a smaller deviation in half-wave potential (Delta E-1/2 = 18 mV) compared to the Pt/C catalyst (Delta E-1/2 = 50 mV) even after 5k potential cycling under similar conditions. The relatively lower ionic diffusion and charge transfer resistance at the electrode/electrolyte interface by the MnBN/C-75 electrode support to our claim regarding a higher electrocatalytic activity. Thus, the presence of Mn3+ ions in the form of MnOOH (during composite formation) along with both h-BN support and KB carbon at the electrode surface contributes immensely in boosting the electrocatalytic activity. Thus, it could be a promising electrocatalyst, if employed in the cathode compartment of low-temperature fuel cells to lead faster ORR kinetics.