Built-in Electric Field Enables Relay Catalysis in Ni4Mo/MoO2 Mott-Schottky Heterojunction for Selective Methanol-to-Formate Electrooxidation

Comprehensive Summary The selective electrooxidation of methanol to formate is a kinetically complex process involving multiple intermediates ( e.g ., *CH 3 O, *CHO, *OH), whose adsorption energies are difficult to regulate simultaneously. Here, we report a conceptually new electric-field-directed relay catalysis strategy based on a Ni 4 Mo/MoO 2 Mott-Schottky heterojunction. Using a combination of UPS, XPS, and XAFS, we demonstrate that the built-in electric field (BIEF) drives directional electron transfer from metallic Ni 4 Mo to semiconducting MoO 2 , creating spatially separated electron-deficient Ni sites and electron-rich MoO 2 interfaces. Operando FTIR and Raman spectroscopy directly visualize the dynamic evolution of intermediates, revealing a relay mechanism: Ni sites promote *CH 3 O adsorption and C–H/O–H bond cleavage, while MoO 2 enhances *OH supply to accelerate *CHO oxidation. DFT calculations confirm that this BIEF-mediated spatial decoupling lowers the energy barrier of the potential-determining step (*CHO → *HCOOH) from 1.96 eV (Ni 4 Mo) to only 0.76 eV. Consequently, the obtained catalyst achieves a peak current density of 345.2 mA·cm –2 with >97% Faradaic efficiency for formate. This work establishes a new paradigm for designing heterojunction electrocatalysts that leverage interfacial electric fields to orchestrate multi-step reaction pathways with high selectivity.