Oxygen Electrocatalysis by [Au₂₅(SR)₁₈]: Charge, Doping, and Ligand Removal Effect

Abstract

Considering the promising prospects of Au25(SR)18 q and its alloy clusters in numerous fundamental catalysis research studies derived from their well-defined structures, developing a deep understanding of the structure–property correlation becomes significantly urgent. Herein, we explored a prototype [Au25(SR)18] q cluster, monoatom-doped bimetallic [MAu24(SR)18] q clusters (M = Pt, Pd, Ag, Cu, Hg, or Cd), and their singly deligated M-exposure and S-exposure systems as electrocatalysts toward O2 reduction reaction (ORR) at the acidic medium. Theoretical simulations reveal that the fully ligand-protected clusters prefer H2O2 formation through the two-electron (2e–) mechanism, whereas the dethiolated clusters prefer to proceed via the four-electron (4e–) pathway for H2O production. Among them, a single Hg substitution at the staple site, namely, fully ligated [HgAu24(SCH3)18]0–O and dethiolated [HgAu24(SCH3)17]0–O with an exterior −SCH3 removal has great potential to realize high-efficiency 2e– and 4e– ORR, with an ultralow overpotential of 0.08 and 0.43 V, respectively. The correlation between adsorption of oxygenated intermediates and Bader charge as well as active metal d-band center sheds light on the underlying origin of selectivity and activity. Besides, the analysis of projected density of states suggests that monoatom doping has a mild modification to the s-bands of Au, but the removal of the −SR ligand can obviously amend the electronic structure of Au-s states. Particularly, in contrast to the strong d-electron effect in Au25 q and other doped MAu24 q clusters, the s-electron effect from the staple-doped Hg atom shows great promise in optimizing the intermediate adsorption and functions as a distinguished electrocatalyst for O2 reduction. These insights provide useful guidelines for the design of high-efficiency metal nanocluster electrocatalysts by implementing late-transition metal or p-block metal with a strong s- or p-electron effect to achieve superior ORR activity.

First-Principles Studies on Electrocatalytic Activity of Novel Two-Dimensional MA2Z4 Monolayers toward Oxygen Reduction Reaction

“…It is found that Pt(111) tends to follow the 4e − pathway, and the calculated limiting potential in our case is 0.66 eV, which slightly deviates by about 0.13 V compared to the previously reported value (0.79 eV). Note that herein only 27 MA 2 Z 4 with U L less than 1.23 V are displayed (Figure 4a S3, while the optimal ΔG OOH* should be around 3.69 eV), 62 111) catalyst (U L = 0.79 V), indicating its promising applications as a highly efficient ORR electrocatalyst. We further examined the ORR performance of the most promising CrGe 2 As 4 catalyst both with and without dispersion correction.…”

“…Analysis of the O* adsorption strength (Table S4) revealed that they all exhibit very strong O* binding (0.81 eV for MoSi 2 P 4 , 0.90 V for WSi 2 P 4 , and 0.71 eV for WGe 2 P 4 , vs the optimal ΔG O* of 2.46 eV). 62 Such a high overpotential and ORR activity. The active sites of the screened catalysts are all located at the surface As atoms.…”

“…Most of the MA 2 Z 4 , however, has small U L (0.1–0.4 V) and shows very low ORR activity. The main reason is that the N-terminated MA 2 N 4 has relatively weak OOH* adsorption (mostly around 4.35–5.28 eV from Table S3, while the optimal Δ G OOH* should be around 3.69 eV), which causes the first step hydrogenation from O 2 to OOH* (the potential-determining step) have to overcome a very high barrier; while for P-terminated MA 2 P 4 and some of the As-terminated MA 2 As 4 , they have too strong binding for O* (around 0.49–1.62 eV vs the optimal Δ G O* of 2.46 eV) or OH* (around −0.39–0.41 eV vs the optimal Δ G OH* of 1.23 eV), which makes the third (O* → OH*) or fourth step (OH* → H 2 O) reduction becomes very difficult. Among them, only CrGe 2 As 4 ( U L = 0.74 V), VGe 2 As 4 ( U L = 0.62 V), NbSi 2 As 4 ( U L = 0.68 V), and VSi 2 As 4 ( U L = 0.62 V) are screened out to show promising electrocatalytic potential of ORR.…”

“…At the equilibrium potential of U = 1.23 V, however, the above three MA 2 Z 4 have to overcome a significantly high barrier for the reduction of O* to OH* (the potential-determining step), which corresponds to a very high overpotential (η) of 1.34, 1.51, and 1.19 V (Table S7), respectively. Analysis of the O* adsorption strength (Table S4) revealed that they all exhibit very strong O* binding (0.81 eV for MoSi 2 P 4 , 0.90 V for WSi 2 P 4 , and 0.71 eV for WGe 2 P 4 , vs the optimal Δ G O* of 2.46 eV) . Such a high overpotential and the strong O* binding indicate that MoSi 2 P 4 , WGe 2 P 4 , and WSi 2 P 4 cannot been employed as viable ORR electrocatalysts, and their surfaces can be easily oxidized that poisoned the catalysts.…”

Understanding the Single Atom Doping Effects in Oxygen Reduction with Atomically Precise Metal Nanoclusters

“…On the contrary, the well-defined NCs with resolved atomic structures are ideal model catalysts not only for the experimental probing of the key factors − but also for computational modeling, thus providing opportunities for deeper mechanistic insight . Recently, Sun et al predicted the doping effects on the ORR based on gold NCs through theoretical simulations, indicating that the doping may significantly change the reaction mechanism of the ORR . However, direct experimental evidence of doping effects in atomically precise metal NCs is yet to be found, which will also provide opportunities for understanding more fundamental aspects.…”