•The CM particle electrode with rich in N, P was prepared using duckweed.•Ru catalyst was dispersed uniformly on CM-650 with amorphous.•The Ru/CM-650 exhibited high activity for electrocatalytic dechlorination of DCF. In order to improve degradation efficiency and reduce electrode cost, carbon microspheres (CM) particle electrode was prepared from readily available duckweed as a raw material for electrocatalytic hydrodechlorination. The surface structures and chemical characteristics of the CM were regulated by adjusting the pyrolysis temperature. When pyrolysis was performed at 650 °C, carbon microspheres (CM-650) with large surface areas that are rich in heteroatoms (N, P) and show high electrical conductivity are obtained. After the Ru catalyst was supported, the Ru/CM-650 as particle electrode forming a three-dimensional (3D) electrochemical reaction system exhibits high electrocatalytic performance for diclofenac (DCF) hydrodechlorination with dechlorination efficiency of more than 90% in 150 min. Furthermore, the Ru/CM-650 has good stability for repeated use, which is attributed to the synergistic interaction between N and P elements improving the stability of the catalyst.