Controlling the formation of nanosized branched nanoparticles with high uniformity is one of the major synthetic challenges to achieve nanocatalysts with improved activity and stability. Using a cubic-core hexagonal-branch mechanism to form highly monodisperse branched nanoparticles we vary the length of the nickel branches. Lengthening the nickel branches, with their high coverage of active facets, is shown to improve activity for electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) as an example for biomass conversion.The synthesis of well-defined 3D nanostructures has been achieved for the fabrication of noble metal nanoparticles. [1][2][3][4][5] As the focus of energy conversion shifts towards earth abundant transition metal catalysts and alkaline electrolytes, approaches are needed to synthesize highly defined and uniform nanoparticles made of first row transition metals. A critical feature for uniform nanoparticles is branch dimension and the surface faceting. [5,6] Ideally for catalysis, nanoparticles should have branch diameters of less than 25 nm to achieve highest possible surface area. [7,8] The synthesis also needs to control branch length to enable high exposure of specific active facets. [9][10][11] This is vital because well-defined faceting determines the active sites available for catalysis, as has shown to be crucial for branched nanoparticle catalysts. [1,2,12]