The electrocatalytic performance of highly conducting Nickel phosphate (NiPh)/carbon composite catalyst is investigated for the oxidation of formaldehyde in alkaline solution. The NiPh nanoparticles are synthesized by a cost-effective one-pot method, which is based on refluxing nickel and phosphate precursors at 90 degrees C. Inks of the composite catalyst are pro-duced by mixing NiPh nanoparticles with carbon conductive additives (CCA) and Nafion oil. Then, the ink is cast then dried on the glassy carbon electrode. Systematic study is performed to investigate the effect of varying the CCA loading on the electrochemical oxidation of formaldehyde. The best catalytic performance is obtained for NiPh/CCA composite catalyst containing 20 wt% of CCA (NiPh/CCA-20 wt%). The physicochemical properties of the com-posite catalysts are investigated and analyzed by field-emission scanning electron micro-scopy (FE-SEM), Energy Dispersive x-ray Spectroscopy (EDX) and X-ray diffraction (XRD). Also, the N-2 adsorption/desorption isotherms are recorded and the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods are used to calculate the specific surface area and pore size distribution. The electrocatalytic performance of the NiPh/CCA composite was compared to the pristine NiPh for the oxidation of formaldehyde in alkaline solution. Electrochemical impedance spectroscopy technique is used to study the electrical conductivity of the composite catalysts. Additionally, cyclic voltammetry and chronoamperometry techniques are used to calculate key parameters such as surface coverage (Gamma) of Ni2+/Ni3+ species, the diffusion coefficient of the formaldehyde (D) and the catalytic rate constant (k(cat)). (A) over tilde, D and k(cat) values for the NiPh/CCA-20 wt% catalyst are 5.95 x 10(-5) mmol cm(-2), 1.08 x 10(-4) cm(2) s(-1) and 2.59 x 10(7 )cm(3) mol(-1) s(-1) respectively. Both Gamma and k(cat) parameters are used to identify the optimum composition of the catalyst. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.