Optimizing the Spatial Density of Single Co Sites via Molecular Spacing for Facilitating Sustainable Water Oxidation

Abstract

Advances in single-atom (-site) catalysts (SACs) provide a new solution of atomic economy and accuracy for designing efficient electrocatalysts. In addition to a precise local coordination environment, controllable spatial active structure and tolerance under harsh operating conditions remain great challenges in the development of SACs. Here, we show a series of molecule-spaced SACs (msSACs) using different acid anhydrides to regulate the spatial density of discrete metal phthalocyanines with single Co sites, which significantly improve the effective active-site numbers and mass transfer, enabling one of the msSACs connected by pyromellitic dianhydride to exhibit an outstanding mass activity of (1.63 ± 0.01) × 105 A·g–1 and TOFbulk of 27.66 ± 1.59 s–1 at 1.58 V (vs RHE) and long-term durability at an ultrahigh current density of 2.0 A·cm–2 under industrial conditions for oxygen evolution reaction. This study demonstrates that the accessible spatial density of single atom sites can be another important parameter to enhance the overall performance of catalysts.

Remodeling the Electronic Structure of Metallic Nickel and Ruthenium via Alloying in a Molecular Template for Sustainable Hydrogen Evolution

“…Alloying with platinum group metals (PGMs) is a versatile strategy to boost the catalytic activity of nonprecious transition metals. − Alloys are available to tailor the reactivity of the active sites to optimize the adsorption/desorption of catalytic intermediates, thereby drastically lowering the activation energy barrier (Figure a). − Ruthenium (Ru) is not only the cheapest PGMs but also possesses hydrogen evolution activity close to that of Pt, representing an ideal alloying metal for performance enhancement. − Normally, small-sized nanoalloys (<5 nm) not only possess high atomic utilization and distinctive electronic structures but also feature abundantly exposed unsaturated active sites and high specific surface areas, thus presenting remarkable catalytic properties. , At present, alloys are prone to agglomerate to form large-sized particles under the general thermal synthesis conditions, which severely limits their catalytic activity, resulting in rarely alloyed catalysts capable of yielding ampere-level current densities for HER at low overpotentials. − Therefore, it remains a challenge to construct highly dispersed, small alloy nanostructures with high performance. Porous organic polymers (POPs) are tunable molecular materials formed through covalent bonding of organic monomers, serving as molecular templates for fabricating various types of metal nanostructures. − POPs can anchor metal species with the coordination atoms on the frameworks, limiting their agglomeration and growth in thermal synthesis, thus decreasing the size of metal nanoparticles (NPs). , In addition, the porous carbon layers derived from POPs function as favorable carriers for metal NPs and stabilize their active structures. , Therefore, POPs are expected to furnish promising molecular templates for architecting small alloys with great dispersibility.…”

Efficient Acidic Photoelectrochemical Water Splitting Enabled by Ru Single Atoms Anchored on Hematite Photoanodes

“…Recently, single-atom catalysts (SACs) have demonstrated impressive performance in various catalytic reactions, such as CO 2 reduction, nitrate electroreduction to ammonia, and methane conversion. − SACs are characterized by the complete exposure of active sites through isolated metal atoms, resulting in a high metal utilization and an increased active surface area. The strong interactions between the fully dispersed metal atoms and the carrier material give SACs a unique electronic structure, enabling optimized reaction interfaces. − To date, single-atom species of Ru and Ir have been predominantly documented on substrates like carbon or metal alloys, with a paucity of studies on their deployment on photoanodes such as hematite. , Integrating single noble-metal atoms onto hematite photoanodes holds great potential for accelerating the OER kinetics while significantly reducing the loading mass of precious metals but presents a significant challenge. Herein, we developed a straightforward impregnation–annealing method to engineer Ru single atoms directly anchored onto hematite for efficient PEC water oxidation in acidic electrolytes.…”