Single‐Site, Single‐Metal‐Atom, Heterogeneous Electrocatalyst: Metal–Organic‐Framework Supported Molybdenum Sulfide for Redox Mediator‐Assisted Hydrogen Evolution Reaction

Abstract

Synthesis of single-site catalysts, whereby the local structure and surrounding chemical environments are identical, has been challenging, particularly in heterogeneous catalysis, as the support often presents spectrum of chemically distinct binding sites. Yet, the above criteria are crucial in attributing the apparent catalytic performance to the structural motif. The presented work augments on our previous work using monometallic molybdenum sulfide tethered within a zirconium-based metal-organic framework (MOF), NU-1000; the monometallic nature enables all presented sites to be catalytically addressable. As the molybdenum sulfide species resided within two distinct pores (micro-and mesopores) of the MOF support, we have imparted uniformity in the local chemical environment by reducing the pore heterogeneity down to a single mesopore. Single-site and single-atom nature of the candidate catalyst was established via X-ray diffraction measurements. Redox mediators were implemented, which, under reductive potentials, provide reduced species; they can effectively deliver the necessary reducing equivalences to the catalytic units that can otherwise not be addressed electrochemically due to the low electron mobility within the framework. Our results indicate the micropore-allocated molybdenum sulfide is approximately four times more active as that in mesopores, whereas its catalytic mechanism is identical, underscoring the importance of controlling chemical environment beyond the active site.

Pyrene-based metal organic frameworks: from synthesis to applications

“…The thickness and morphology of the films can be controlled by simply adjusting the depositing time and applied potential. 285 These thin films can be used as molecular switches, 286,287 biasswitchable permselectivity anions membranes, 279 and electrocatalysts for OER, 283,288 HER, 289,290 and CO 2 reduction. 291 Among these applications, electrocatalytic OER and HER are of interest since electrocatalytic water splitting can provide a much more sustainable and carbon-neutral route for energy generation.…”

“…Mechanistic studies showed that overall control of the rate of catalysis can be defined by mediator-to-catalyst electron transfer, solution-to-catalyst proton transfer, or both. 289,290 Kung et al 283 performed the chemical growth of uniform thin films of NU-1000 on transparent fluorine-doped tin oxide (FTO) conducting glass, followed by the deposition of Co(II) ions, resulting in the oxidation catalyst Co-AIM NU-1000. Cyclic voltammetric (CV) experiments showed that Co-AIM-NU-1000 is electrochemically active.…”

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

“…In view of the role of mononuclear, binuclear and/or cluster-based metal-sulfur species as electron carriers and as cofactors for enzyme-catalysed reduction of protons to molecular hydrogen, and N 2 reduction to ammonia, replacing or converting the above metal-oxy species with or to metal-sulfur (sulfide, disulfide, thiolate, sulfhydryl) species could render many of these species functional for MOFintegrated reductive catalysis. 98,99,[319][320][321][322][323][324] Summarized in Fig. 57 are examples based on grafting single-metal-atom Mo(SH) 2 units to an open site on an eight-connected MOF.…”

Metal–Organic‐Framework‐Derived Nanostructures as Multifaceted Electrodes in Metal–Sulfur Batteries

“…Compared with traditional inorganic porous catalyst and nanometer catalyst, MOFs with evenly dispersed catalytic sites, large specific surface area, etc., offer better catalytic performances. [ 164–167 ] It is feasible to design MOFs with different hierarchies and rich polarity/catalytic sites. For example, the Jiang group has developed an aluminum‐based porphyrinic MOF (Al‐TCPP) to stabilize a single platinum site through strong chemical affinity with pyrrolic N atom, [ 168 ] which provide highly effective charge transfer tunnels and thereby possess potential application in electrocatalysis ( Figure a).…”