The electrochemical behavior of B(III) on a molybdenum electrode in NaCl–KCl–KBF₄ molten salt at 1023 K is investigated and the diffusion coefficients of B(III) are calculated by cyclic voltammetry, square wave voltammetry and chronopotentiometry, respectively. The results show that the reduction of B(III) to B(0) is a diffusion-controlled single-step three-electron transfer reaction and the diffusion coefficient of B(III) is calculated to be 4.3 ± 0.4 × 10⁻⁵ cm² s⁻¹ at 1023 K by cyclic voltammetry. An individual spheroidal aggregate boron coating is obtained by galvanostatic electrolysis.