Phase‐Engineered MoS 2 Quantum Monolayer Catalysts

ABSTRACT Single‐atom catalysts with 100% atomic efficiency represent a frontier in heterogeneous catalysis, yet they face low loading density of active species (normally < 5.0 wt.%), poor stability, and difficulties in low‐cost synthesis. Here, we present a new type of catalyst model—phase‐engineered quantum‐monolayer catalyst, as a complementary catalyst architecture that offers high‐density accessible atoms and enables versatile phase/interphase engineering for catalysis. As a prototype (in our 13‐type quantum monolayer library), our fabricated MoS 2 quantum‐monolayer catalysts are one molecule‐layer thick (∼0.8 nm), quantum‐sized (< 6 nm in the lateral size), and phase controllable (switchable freely among metallic 1T, semiconducting 2H, and hybrid phase of metallic‐semiconducting 1T‐2H). They can be synthesized on a large scale (experimentally demonstrated at a 20 g scale) with a high quantum‐monolayer yield (>99%) and product recovery ratio (>95%); can be stored independently and stably (at 4°C or in an inert atmosphere) for more than 6 months; can be easily processed into customized structures by solution deposition technologies; and have the potential to be used as a catalyst or co‐catalyst for photo‐, electro‐, and thermo‐chemical conversions. We demonstrate their potential for photochemical H 2 , syngas, and NH 3 production with high performance and stability.