Boost reactivity of tri-iodide reduction electrode by highly faceted octahedral PtNi nanocrystals

•PtxNi1-x octahedral catalyst were chemically prepared for the I3- reduction in DSSCs.•The crystallographic orientation of PtNi octahedron was characterized via on-axis TDK techniques.•The I3- reduction activity is in a sequence of Pt4Ni6 > Pt5Ni5 > Pt7Ni3 > Pt thin film.•The maximum PCE of DSSCs with Pt4Ni6 octahedra achieve 10.10%.•Electrochemical and photovoltaic results reveal the advantage of PtNi octahedral CEs.•High coverage of {111} facets of CEs surpasses the alloying composition of CEs in the I3- reduction.