Intercalated layered materials offer distinctive properties and serve as precursors for important two-dimensional (2D) materials. However, intercalation of non–van der Waals structures, which can expand the family of 2D materials, is difficult. We report a structural editing protocol for layered carbides (MAX phases) and their 2D derivatives (MXenes). Gap-opening and species-intercalating stages were respectively mediated by chemical scissors and intercalants, which created a large family of MAX phases with unconventional elements and structures, as well as MXenes with versatile terminals. The removal of terminals in MXenes with metal scissors and then the stitching of 2D carbide nanosheets with atom intercalation leads to the reconstruction of MAX phases and a family of metal-intercalated 2D carbides, both of which may drive advances in fields ranging from energy to printed electronics.
The
development of abundant, cheap, and highly active catalysts
for the hydrogen evolution reaction (HER) and oxygen evolution reaction
(OER) is important for hydrogen production. Nanolaminate ternary transition
metal carbides (MAX phases) and their derived two-dimensional transition
metal carbides (MXenes) have attracted considerable interest for electrocatalyst
applications. Herein, four new MAX@MXene core–shell structures
(Ta2CoC@Ta2CT
x
,
Ta2NiC@Ta2CT
x
, Nb2CoC@Nb2CT
x
, and Nb2NiC@Nb2CT
x
), in which
the core region is Co/Ni-MAX phases while the edge region is MXenes,
have been prepared. Under alkaline electrolyte conditions, the Ta2CoC@Ta2CT
x
core–shell
structure showed an overpotential of 239 mV and excellent stability
during the HER with MXenes as the active sites. For the OER, the Ta2CoC@Ta2CT
x
core–shell
structure showed an overpotential of 373 mV and a small Tafel plot
(56 mV dec–1), which maintained a bulk crystalline
structure and generated Co-based oxyhydroxides that formed by surface
reconstruction as active sites. Considering rich chemical compositions
and structures of MAX phases, this work provides a new strategy for
designing multifunctional electrocatalysts and also paves the way
for further development of MAX phase-based materials for clean energy
applications.
Transition
metal (oxy)hydroxides are recognized as the most effective
non-noble metal electrocatalysts for the alkaline oxygen evolution
reaction (OER). However, their electrical conductivity and durability
are insufficient for the development of electrochemical energy devices.
Thus, constructing more compact and stable transition metal-based
composite materials while maintaining high activity is still desperately
needed. In this study, we propose a potent approach for producing
highly active sites via alloying transition metals with carbon elements
evolved from the MAX phases. We for the first time found an activation
paradigm for such a phase (V2(Co
x
Sn1‑x
)C) via an OER in situ
polarization process. The mechanism is proposed as the Co element
in the A site significantly facilitates the structural evolution of
the pristine V2SnC phase. Compared with typical electrodeposited
cobalt hydroxide (Co–H), such a MAX-derived catalyst exhibits
better OER activity and lower valence charge transition potential
owing to its unique nanocomposite structure, more exposed active sites,
and better electric conductivity. Furthermore, the preparation of
this catalyst is applicable to nickel foams. Our investigation confirmed
its long-term stability and superior activity over most reported Co-based
catalysts. This unique structural evolution route provides a potentially
generalizable strategy for MAX phases as efficient electrocatalysts.
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