Unveiling of Unpaired Surface Spins Regulated Magnetism in 2D α-Te Nanosheets: an Implication on Magnetoelectric Driven Hydrogen Evolution.

Quasi-2D tellurium (Te) unlocks surface spins (of valence 5p4 electrons) of tunable ferromagnetic order and response to strain-engineered electronic properties of widespread applications. In spin-orbit coupling, the inversion symmetry is broken in a 1S0 → 3S1 spin-transition of the ground electronic state, a synergetic pathway to charge spin-order under applied driving forces. The surface magnetism, combined with the ferroelectricity, gives a giant magnetoelectric response (absent in 1S0 bulk Te state) that is explored to boost the H2 evolution reaction (HER) with 2D α-Te as a synergetic catalyst. High-quality 2D α-Te synthesized as nanosheets is ordered primarily along (001) facets at duly enhanced d001 atomic spacing in the 5s2-Te lone pair electrons (diamagnetic) are spaced (Coulomb repulsion) via the 5p2 unpaired spins. Poled 2D α-Te in small fields, such as 30 mT, presents a HER overpotential that is decreased up to 100 mV, while the Tafel slope is declined up to 138 from 211 mV dec-1 for the bulk sample. The electrochemical stability of 2D α-Te is found quite impressive with 93% current retention (71% if non-magnetized) under chronoamperometric conditions. The results present that the 2D α-Te plays a game-changing role towards sustainable energy technologies, spintronics, and next-generation magnetoelectric devices.