Theoretical Insights into the Selectivity of Single-Atom Fe–N–C Catalysts for Electrochemical NO<i><sub><i>x</i></sub></i> Reduction
Yao Tan, Junwei Fu, Tao Luo, Kang Liu, Min Liu
Abstract
Single-atom Fe–N–C catalysts have attracted significant attention in the NO x reduction reaction (NO x RR). However, the origin of their selectivity in the NO x RR remains unclear, impeding further advancements in application. Herein, we investigate the potential-driven competitive mechanism for NH 3 and NH 2 OH production in the NO x RR over single-atom pyridinic-FeN 4 and pyrrolic-FeN 4 sites using constant-potential density functional theory calculations. The origin of selectivity in the NO x RR is linked to the switching of Fe 3 d orbitals as they interact with intermediates. The selectivity between NH 3 and NH 2 OH is determined by the applied potentials. The pyridinic-FeN 4 predominantly generates NH 3 at higher reduction potentials (−0.6 to −1.2 V, vs SHE), while NH 2 OH is favored at lower reduction potentials (0.6 to −0.6 V). The pyrrolic-FeN 4 shows a similar potential-dependent product distribution, with a crossover potential of −1.0 V. The selectivity-determining intermediates (SDIs) in the NO x RR are *NH 2 OH and *NH 2 + *OH. The potential-dependent selectivity is governed by the switching of Fe 3 d orbitals interacting with SDIs, from dumbbell-shaped Fe 3 dz 2 to four-leaf clover-like Fe 3 dxz, 3 dyz, and 3 dx 2 -y 2, which plays a crucial role in controlling product distribution based on applied potentials. These findings offer new insights into the product selectivity of single-atom catalysts for the NO x RR.