An Oxygen‐Insensitive Hydrogen Evolution Catalyst Coated by a Molybdenum‐Based Layer for Overall Water Splitting

For overall water‐splitting systems, it is essential to establish O 2 ‐insensitive cathodes that allow cogeneration of H 2 and O 2 . An acid‐tolerant electrocatalyst is described, which employs a Mo‐coating on a metal surface to achieve selective H 2 evolution in the presence of O 2 . In operando X‐ray absorption spectroscopy identified reduced Pt covered with an amorphous molybdenum oxyhydroxide hydrate with a local structural order composed of polyanionic trimeric units of molybdenum(IV). The Mo layer likely hinders O 2 gas permeation, impeding contact with active Pt. Photocatalytic overall water splitting proceeded using MoO x /Pt/SrTiO 3 with inhibited water formation from H 2 and O 2 , which is the prevailing back reaction on the bare Pt/SrTiO 3 photocatalyst. The Mo coating was stable in acidic media for multiple hours of overall water splitting by membraneless electrolysis and photocatalysis.