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

Abstract

The selective electrooxidation of methanol to formate is a kinetically complex process involving multiple intermediates (e.g., *CH₃O, *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 Ni₄Mo/MoO₂ 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 Ni₄Mo to semiconducting MoO₂, creating spatially separated electron-deficient Ni sites and electron-rich MoO₂ interfaces. Operando FTIR and Raman spectroscopy directly visualize the dynamic evolution of intermediates, revealing a relay mechanism: Ni sites promote *CH₃O adsorption and C–H/O–H bond cleavage, while MoO₂ 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 (Ni₄Mo) 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.