Phase-Engineered MoS2 Quantum Monolayer Catalysts.

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 MoS2 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 H2, syngas, and NH3 production with high performance and stability.