Single-Atom Catalysts Electrostatically Stabilized by Ionic Liquids

A universal and scalable transformation of bulk metals into single-atom catalysts in ionic liquids

Single-atom catalysts (SACs) with maximized metal atom utilization and intriguing properties are of utmost importance for energy conversion and catalysis science. However, the lack of a straightforward and scalable synthesis strategy of SACs on diverse support materials remains the bottleneck for their large-scale industrial applications. Herein, we report a general approach to directly transform bulk metals into single atoms through the precise control of the electrodissolution-electrodeposition kinetics in ionic liquids and demonstrate the successful applicability of up to twenty different monometallic SACs and one multimetallic SAC with five distinct elements. As a case study, the atomically dispersed Pt was electrodeposited onto Ni3N/Ni-Co-graphene oxide heterostructures in varied scales (up to 5 cm × 5 cm) as bifunctional catalysts with the electronic metal-support interaction, which exhibits low overpotentials at 10 mA cm-2 for hydrogen evolution reaction (HER, 30 mV) and oxygen evolution reaction (OER, 263 mV) with a relatively low Pt loading (0.98 wt%). This work provides a simple and practical route for large-scale synthesis of various SACs with favorable catalytic properties on diversified supports using alternative ionic liquids and inspires the methodology on precise synthesis of multimetallic single-atom materials with tunable compositions.

Regulation of Electronic Structures to Boost Efficient Nitrogen Fixation: Synergistic Effects between Transition Metals and Boron Nanotubes

Borophene possesses outstanding physical and chemical properties and thus demonstrates great application potential in catalysis. However, the lack of a controllable strategy for regulating the electronic structures of borophene for efficient catalysis limits the exploration of this material for a "black-box" model. Herein, taking advantage of the synergistic effects between metals and boron nanotubes (BNT), we report a core-shell structure that encapsulates early transition-metal nanowires into BNT (TMs@BNT) to improve the inherent electronic structures of primitive borophene for an efficient electrochemical nitrogen reduction reaction (eNRR). These filled BNT with disconnected π conjugation and vacant boron (B) p_z orbitals enable the regulation of electronic states of B atoms in spatial extent and occupancy that has a great effect on the adsorption strength of intermediates. Using first-principles calculations, we demonstrate that the *N₂H adsorption energy (ΔE_*N2H) is strongly correlated with the intrinsic activity trends and that the variation of ΔE_*N2H is attributed to the distribution of 2p states and charge of B atoms. Finally, we utilize the coupling of the d 2p states between B atoms and metals to obtain a quantitative explanation for synergistic effects and conclude that metals with a lower d-band center (ε_TM d) raise the average 2p state energy (ε̅_2p) of B through two-level quantum coupling, which is the physical origin of this interaction. Therefore, two candidates (Mo@BNT and W@BNT) with lower ε_TM d are screened, benefiting from their high eNRR activity (limiting potentials of -0.75 and -0.77 V, respectively) and high selectivity. This work explores the activity origin, constructs a bridge between electronic structures and activity trends, and paves the way for future eNRR studies.

NP monolayer supported transition-metal single atoms for electrochemical water splitting: a theoretical study

The development of cost-effective and highly efficient electrocatalysts for water splitting is highly desirable but remains an ongoing challenge. Numerous single-atom catalysts (SACs) have achieved satisfactory performances in this area; however, non-carbon metal-free substrates have been rarely explored. Herein, we report a series of single-metal atoms supported on a novel two-dimensional NP monolayer as promising electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) by theoretical calculations. Our results disclose that Ti@NP, V@NP and Ir@NP exhibit desirable catalytic activity for the HER with extremely low of -0.004, -0.051, and 0.017 eV, respectively. More importantly, the calculated activation barriers for the Tafel reactions of these SACs are much lower than those for the benchmark Pt catalysts. In addition, Pt@NP shows the lowest η^OER of 0.495 V, followed by Rh@NP (η^OER = 0.548 V), which are even superior to that of state-of-the-art IrO₂. This work highlights the potential application of metal-free supports in SACs, which also further enriches the application of a NP monolayer in other related electrochemical processes.

Reductive Upgrading of Biomass-Based Levulinic Acid to γ-Valerolactone Over Ru-Based Single-Atom Catalysts

With the great adjustment of world industrialization and the continuous improvement of energy consumption requirements, the selective conversion of biomass-based platform molecules to high-value chemicals and biofuels has become one of the most important topics of current research. Catalysis is an essential approach to achieve energy-chemical conversion through the “bond breaking-bond formation” principle, which opens a broad world for the energy sector. Single-atom catalysts (SACs) are a new frontier in the field of catalysis in recent years, and exciting achievements have been made in biomass energy chemistry. This mini-review focuses on catalytic conversion of biomass-based levulinic acid (LA) to γ-valerolactone (GVL) over SACs. The current challenges and future development directions of SACs-mediated catalytic upgrading of biomass-based LA to produce value-added GVL, and the preparation and characterization of SACs are analyzed and summarized, aiming to provide theoretical guidance for further development of this emerging field.