Synergy of Substrate Chemical Environments and Single-Atom Catalysts Promotes Catalytic Performance: Nitrogen Reduction on Chiral and Defected Carbon Nanotubes

Abstract

The catalytic activities of single-atom catalysts (SACs) are strongly influenced by the local chemical environments of their substrates, by which the electronic structures of the SACs can be effectively tuned. Together with the freedom of available reactive metallic centers, it would be feasible to maximize the catalytic performance by means of a synergetic optimization in the chemical space spanned by the features of both the substrate and the catalytic center. In this work, using first-principles calculations, we systematically assessed the synergetic effect between the substrate geometric/electronic structures and the catalytic centers on the electrocatalytic nitrogen reduction reaction (NRR). Carbon nanotubes with different chirality, defects, and chemical functionalization were used to support 15 transition metal atoms. Three SACs, TiN4CNT(3,3), TiN4CNT(5,5), and VN4CNT(3,3), simultaneously possess high NRR selectivities (w.r.t hydrogen evolution) and low overpotentials of 0.35, 0.35, and 0.37 V, respectively. Electronic structure analysis elucidated that larger metal atoms anchored on CNTs with higher curvature and doped by N atoms facilitate the rupture of the N–N bond in *NH2NH2 to lower the overpotentials. The synergy of substrate chemical environments and single atomic catalysis is a promising strategy to optimize the catalytic performance.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

“…To ensure a stable N 2 adsorption (Δ G (*N 2 ) < 0), the focus should be directed specifically toward SACs within the shaded blue region. The electronic structure analysis elucidated that larger metal atoms anchored on CNTs with higher curvature and doped with N atoms facilitated the rupture of the N–N bond in *NH 2 NH 2 to lower the overpotentials . In more detail, the authors elucidated the interaction between M-dyz and N-py of *NH 2 NH 2 by employing band diagrams, as depicted in Figure b, c. These diagrams illustrate the rupture and integrity of the N–N bond.…”

“…The blue shadow represents the N 2 stable adsorption region, (b, c) Band structure of M d yz orbital, N-p y orbital of the NH 2 NH 2 molecule, and their interaction of the *NH 2 NH 2 adsorption for (b) TiN 4 CNT(5,5) and (c) VN 4 CNT(5,5). Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”

Tailoring of Three-Atom Metal Cluster Catalysts for Ammonia Synthesis

“…Based on previous studies [42,46,47], the formation of *NNH and the last hydrogenation step to form *NH 3 via the protonation process are usually considered potential-determining steps (PDS) due to high energy barriers. The values of ∆G N2-N2H and ∆G NH2-NH3 for studied Fe x Mo y -CNs with N 2 side-on adsorption were calculated and shown in Figure 2b.…”