Colloidal　nanocrystal　clusters　constructed　of　abundant　nanocrystal　subunits　possess　immense　potential　for　catalysis　in　fuel　cells　due　to　their　collective　properties　and　novel　functionalities　deriving　from　the　ensemble.　Nevertheless,　the　effects　of　electronic　structure　and　boundary　density　of　subunits　on　their　electrocatalytic　properties　are　rarely　reported.　Herein,　we　report　a　facile　synthesis　of　PtNi　colloidal　nanocrystal　clusters　with　tunable　electronic　structure　and　boundary　density　through　a　one-step　solvothermal　approach.　With　the　increase　of　Ni/Pt　molar　ratio,　more　grain　boundary　and　interspace　are　generated　in　PtNi　colloidal　nanocrystal　clusters,　which　result　in　more　active　sites　and　high　electrochemical　surface　area　for　the　electrooxidation　reactions　of　methanol　and　formic　acid.　Specifically,　the　PtNi3　exhibit　approximately　11.5　(9.6)　times　higher　specific　activity　and　1.8　(1.5)　times　higher　mass　activity　than　those　of　benchmark　Pt/C　for　methanol　(formic　acid)　oxidation.　The　PtNi3　CNCs　also　possess　more　excellent　diffusion　ability　for　MOR　(0.038)　and　FAOR　(0.0082)　compared　with　other　PtNi　CNCs　and　Pt/C.　Combination　of　experiments　and　density　functional　theory　calculation　reveals　the　enhanced　activity　derives　from　the　optimization　of　boundary　density,　d-band　center　and　further　OH　adsorption　ability.　This　approach　provides　a　strategy　to　design　other　colloidal　nanocrystal　clusters　with　excellent　electronic　and　surface　structure　for　direct　fuel　cell　applications.　(C)　2019　Elsevier　Inc.　All　rights　reserved.