Rui Gusmão

Considerable improvements in the electrocatalytic activity of 2D metal phosphorous trichalcogenides (M 2 P 2 X 6 ) have been achieved for water electrolysis, mostly with M II 2 [P 2 X 6 ] 4− as catalysts for hydrogen evolution reaction (HER). Herein, M I M III P 2 S 6 (M I = Cu, Ag; M III = Sc, V, Cr, In) are synthesized and tested for the first time as electrocatalysts in alkaline media, towards oxygen reduction reaction (ORR) and HER. AgScP 2 S 6 follows a 4 e − pathway for the ORR at 0.74 V versus reversible hydrogen electrode; CuScP 2 S 6 is active for HER, exhibiting an overpotential of 407 mV and a Tafel slope of 90 mV dec −1 . Density functional theory models reveal that bulk AgScP 2 S 6 and CuScP 2 S 6 are both semiconductors with computed bandgaps of 2.42 and 2.23 eV, respectively and overall similar electronic properties. Besides composition, the largest difference in both materials is in their molecular structure, as Ag atoms sit at the midpoint of each layer alongside Sc atoms, while Cu atoms are raised to a similar height to S atoms, in the external segment of the 2D layers. This structural difference probably plays a fundamental role in the different catalytic performances of these materials. These findings show that M I (Cu, Ag) together with Sc(M III ) leads to promising achievements in M I M III P 2 S 6 materials as electrocatalysts.