Low‐Valence Metal Single Atoms on Graphdiyne Promotes Electrochemical Nitrogen Reduction via M‐to‐N₂ π‐Backdonation

Abstract

The M‐to‐N2 π‐backdonation weakens the triple bond of N2 and shall promote the sluggish electrochemical nitrogen reduction reaction (ENRR). By using weak σ‐ and π‐donating graphdiyne (GDY) as a supporting material, herein, a versatile approach is described to stabilize low‐valence metal single atoms (SA) on GDY (M SA/GDY; M = Cr, Mo, W, Mn, and Re). Under the rigorous ENRR protocol, an activity trend of Re SA/GDY > Mo SA/GDY > Cr SA/GDY > W SA/GDY >> Mn SA/GDY (no activity) is delivered. Theoretical calculations reveal that the strong M‐to‐N2 π‐backdonation of Re SA/GDY renders a low energy requirement of +0.39 eV for the reductive hydrogenation of *N2 to *NNH, which is considered as the bottleneck of ENRR. A novel NH3 desorption mechanism through N2 or H2O aided ligand exchange mechanism is proposed to facilitate the NH3 desorption from Re SA/GDY with a low energy input of +0.83 eV for the distal and mix pathways. This study expands the scope of low‐valance SA with boosted π‐backdonation capacity and offers new mechanistic insights for ENRR.

Progress of Experimental and Computational Catalyst Design for Electrochemical Nitrogen Fixation

“…Duan and co-workers experimentally reported that steric confinement-induced dense Rh single sites (Rh@GDY) achieve enhanced eNRR activity, and DFT calculations indicated a U L of −0.86 V for eNRR on it . Also, the same research group experimentally revealed an activity trend of Re@GDY > Mo@GDY > Cr@GDY > W@GDY ≫ Mn@GDY for eNRR, while the calculated U L from DFT was −0.83 V on Re@GDY . In addition, Li and co-workers reported that Mo single-site supported on GDY (Mo@GDY) is an efficient eNRR catalyst with a joint experimental and theoretical study .…”

“…129 Also, the same research group experimentally revealed an activity trend of Re@GDY > Mo@GDY > Cr@GDY > W@GDY ≫ Mn@GDY for eNRR, while the calculated U L from DFT was −0.83 V on Re@ GDY. 159 In addition, Li and co-workers reported that Mo single-site supported on GDY (Mo@GDY) is an efficient eNRR catalyst with a joint experimental and theoretical study. 464 Also, Zhai et al theoretically screened a series of TM single sites (Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, and Ag) supported GDY for eNRR, where the Mo@GDY is predicted to be a promising catalyst (U L = −0.33 V following the distal pathway) with high stability and high conductivity.…”

Theoretical and Comparative Analysis of Graphdiyne and Confined Flexible Nitrogen-Doped Graphdiyne-Supported Single-Atom Catalysts for Electrochemical Nitrogen Reduction

“…In the present work, the computed adsorption Gibbs free energy of N 2 is −0.95 eV, and the first protonation step has a Gibbs free energy change of 0.97 eV, in good agreement with the previous study. Moreover, Mo 1 / GDY has been synthesized successfully and proved to be a promising eNRR catalyst. , It is noted that the electron configuration of the early transition metal element Mo is [Kr]­4d 5 5s, with half-full 4 d and 5 s orbitals. The Mo center in Mo 1 /GDY adopts d 2 sp hybridization, which is coordinated by four C atoms in Mo-C 4 moiety.…”

Review on Electrochemical Reduction of Nitrogen by Graphdiyne-Based Catalysts: Recent Advances and Outlook

“…Very recently, our group reported a universal and straightforward method for synthesizing low-valence single atoms on GDY (referred to M SA/GDY; M = Cr, W, Mo, Re, Mn), aiming at maximizing the M-to-N 2 π-backdonation. 85 As shown in Figure 9a, the M SA/GDY catalysts were synthesized by in situ coordination of the relevant metal carbonyl precursors [M(CO) 6-x Cl x ] (x = 0, M = Cr, Mo, and W; x = 1, M = Re and Mn) with the HEB monomer during the Glasercoupling process on the Cu foil. The isolated single-metal atoms can be clearly observed as bright spots in the HAADF-STEM images (Figure 9b).…”