Dimensionality-Tailored Ferromagnetism in Quasi-Two-Dimensional MnSe 2 for the Magnetoelectrochemical Hydrogen Evolution Reaction in Alkaline Media.

The application of an external magnetic field to the cathode shows great promise in facilitating the hydrogen evolution reaction (HER) via water electrolysis. However, the criteria for designing such cathodes are still under investigation. Among various aspects, understanding the effect of different magnetic states of the cathode material is crucial, especially for the HER in alkaline conditions, which possesses different reaction steps compared to that in acidic conditions. Herein, we present MnSe 2 as a cathode material for the magneto-electrocatalytic HER in alkaline media, utilizing its dimension-dependent magnetic phase transition. By tailoring its dimensionality, we have achieved room-temperature ferromagnetism in its quasi-two-dimensional (2D) form, whereas its bulk counterpart exhibits paramagnetism. Upon being subjected to a low external magnetic field of 0.4 T at -182 mV (vs RHE) overpotential, quasi-2D MnSe 2 exhibited a 120% improvement in current density compared to itself at zero magnetic field, while negligible changes were observed in the bulk material. This performance enhancement under a magnetic field could originate from the higher spin polarization of the ferromagnetic catalyst. This work signifies a conceptual advancement of the catalyst's spin state in magnetically enhanced electrocatalytic reaction kinetics.