| 초록 |
The nitrogen cycle is vital for the sustainability of the terrestrial, marine, and atmospheric ecosystems on Earth, and comprises the key stages of nitrogen fixation-nitrification-denitrification. However, the large-scale intensification of a fertilizer-dependent agriculture and the massive combustion of fossil fuels have significantly unbalanced Nature’s nitrogen-cycle. The anthropogenic inflow of nitrogen oxides (NOx) leads to its fast accumulation, causing serious environmental and health problems. Therefore, the electrocatalytic reduction of NOx from renewable energy is a promising strategy to bring the nitrogen-cycle back into balance, alleviating NOx accumulation and at the same time producing useful chemicals. In particular, hydroxylamine (NH2OH) is an interesting compound, involved in the production of caprolactam (the base chemicals for the nylon industry) as well as a potential hydrogen-carrier for the renewable energy society. Here we show iron-nitrogen-doped carbon as an efficient and durable electrocatalyst for selective nitric oxide reduction into hydroxylamine. Using in operando spectroscopic techniques, the catalytic site is identified as isolated ferrous moieties, at which the rate for hydroxylamine production increases in a super-Nernstian way upon pH decrease. Computational multi-scale modeling attributes the origin of unconventional pH dependence to the redox active (non-innocent) property of NO. This makes the rate-limiting NO adsorbate state more sensitive to surface charge which varies with the pH-dependent overpotential. Guided by these fundamental insights, we achieve a Faradaic efficiency of 71% and an unprecedented production rate of 215 μmol cm−2 h−1 at a short-circuit mode in a flow-type fuel cell without significant catalytic deactivation over 50 h operation. |
