Comparative study on the distinct activity for NiFe-based phosphide and sulfide pre-electrocatalysts towards hydrogen evolution reaction

•Evolution of NixFe1-xP and NixFe1-xS eletrocatalysts in HER is investigated.•The distinct HER activity of these electrocatalysts was unveiled.•P dissolution occur for NixFe1-xP in-situ forms highly active α-FeOOH.•S dissolution is mitigated in NixFe1-xS generating less active γ-FeOOH.