The synergy of crystal plane engineering and two-dimensional MXene-mediated Ohmic electron transfer for constructing high-performance sandwich-structured FeS2 oxygen evolution reaction electrocatalysts

The unsatisfactory kinetics of oxygen evolution reaction (OER) severely limits water splitting efficiency, while the prohibitive cost and limited availability of noble metal catalysts constrain their practical applications. Although pyrite-type transition metal sulfides have shown promise as alternative OER catalysts in recent years, their poor intermediate adsorption capacity and low electrical conductivity hinder OER performance improvement. This work presents a density functional theory (DFT)-guided strategy to develop pyrite FeS 2 nanocrystals with active (111) crystal planes, which are further combined with two-dimensional (2D) Ti 3 C 2 T x MXene nanosheets to construct a sandwich-structured FeS 2 /MXene/FeS 2 heterojunction. We demonstrate that the heterojunction exhibits superior OER activity in alkaline environments, requiring a low overpotential of 217 mV to achieve a current density of 10 mA cm −2 . By precisely controlling the exposure of active (111) crystal planes, the distribution of surface adsorption active sites is optimized, significantly enhancing the adsorption capacity of Fe active sites toward OER intermediates and refining the energy barrier of the reaction. Furthermore, the combination of 2D MXene forms Ohmic   contact   interface with FeS 2 , which further reduces the reaction energy barrier by optimizing interfacial electron transfer, particularly lowering the energy barrier for *OOH formation in the rate-determining step (RDS). Additionally, the novel sandwich structure and in-situ formation of surface-active FeOOH endow the heterojunction with excellent stability during OER testing. This work not only elucidates the critical role of crystal planes engineering in enhancing the OER performance of pyrite-type transition metal sulfides, but also offers a new perspective of thinking for designing OER electrocatalysts through the synergy of active crystal planes and Ohmic heterojunction construction.