Further insights into bifunctional mechanism in alkaline hydrogen evolution for hybridized nanocatalysts and general route toward mechanism-oriented synthesis. (March 2021)

• Record Type: Journal Article
• Authors: Jiang, Yan; Sun, Pingping; Sharma, Lekha; Mao, Baoguang; Kakkar, Rita; Meng, Tao; Zheng, Lirong; Cao, Minhua
• Is Part Of: Nano energy. Volume 81(2021)
• Publication Date: 2021-03
• Subjects: Hybridized nanocatalysts -- Bifunctional mechanism -- Real-time EPR -- XAS spectra -- Alkaline HER -- General strategy; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2020.105645
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: The classic bifunctional mechanism derived from single crystal models shows practicability for directing hydrogen evolution reaction (HER) in alkaline media for noble-metal based hybrid catalysts, however, whether it can be extensively applied to non-noble metal nano-hybrid ones remains unclear, due to lacking of effective means to identify reaction active sites and key intermediates. Here we present a representative MoSe2 /CoSe heterogeneous hollow spheres (MoSe2 /CoSe HHSs) as a nano-hybrid catalyst model and demonstrate its atomic-level identification of catalytic active sites toward alkaline HER, by virtue of advanced experimental and theoretical calculating techniques. Real-time electron paramagnetic resonance (EPR) measurements for hydroxyl reveal the promoting effect of the Co species on water dissociation, whereas X-ray absorption spectroscopy (XAS) tests of pre-and post-HER further unravel the formation of high-valence HO-Co sites and MoSe2 -H interactions after the electrolysis, both of which synergistically confirm that MoSe2 /CoSe HHSs follow the classic bifunctional mechanism. Moreover, different from the classic bifunctional mechanism in which there is no substantial interaction between the involved two components, the hybridization of MoSe2 with CoSe also further optimizes hydrogen binding energy (HBE) of MoSe2 revealed by density functional theory (DFT) calculations, demonstrating that both the bifunctional mechanism and HBE should be considered simultaneously when designing low-cost alternatives to noble metal catalysts. Furthermore, a general two-step Ostwald ripening strategy is also proposed for hybridized metal sulfide hollow spheres toward mechanism-oriented material design. Graphical Abstract: ga1 We designed MoSe2 /CoSe HHSs as a model catalyst toward molecular understanding of underlying mechanism in alkaline HER. A series of advanced test techniques and DFT calculations revealed that different from the traditional single crystal Pt catalysts, an integration of bifunctional mechanism and H-binding energy theory is responsible for MoSe2 /CoSe nano-hybrid catalyst. Furthermore, a general two-step Ostwald ripening strategy is also proposed for hybridized metal sulfide hollow spheres, which can guide the mechanism-oriented material design. Highlights: We propose a mechanism-oriented general strategy for hollow-structured hybrids. Real-time EPR and XAS unravel behavior of key intermediates in alkaline HER. DFT calculations show optimized hydrogen binding energy (HBE) for MoSe2 hybrids. Both bifunctional mechanism and HBE theory determine alkaline HER for nanohybrids.