LAUSR

Metal–organic frameworks (MOFs) as cocatalyst for photoelectrochemical (PEC) water splitting is promising but still in its infancy due to the challenge to fabricate high‐quality MOFs coated photoelectrodes. Herein, a successive ionic layer adsorption and reaction (SILAR) method is used to fabricate high‐quality conformal and ultrathin MOFs overlayer with preferred orientation on nanoporous BiVO4 films. 20 molecular monolayers of Co‐MOF coated BiVO4 photoanodes exhibit 3.1‐folds of photocurrent density in comparison with pristine BiVO4. The onset potential shows a negative shift of 320 mV. To further demonstrate the extensibility of SILAR method, the alternative Co‐MOF and Ni‐MOF coated BiVO4 photoanodes deliver an enhanced photocurrent density of 2.97 mA cm−2. The PEC performance achieved rivals the reported results of BiVO4 and MOF hybrid photoanodes. The PEC improvements should be attributed to the high‐quality conformal and ultrathin MOFs overlayer, which can efficiently passivate the surface states of BiVO4, and accelerate the hole transfer through Co‐MOF layer. Three critical roles of Co‐MOF overlayer are elaborately revealed. In contrast, hydrothermally prepared BiVO4/Co‐MOF photoanodes possess inferior PEC performance, such as the photocurrent, and stability. This work clearly demonstrates SILAR method is a simple and efficient approach to realize conformal and ultrathin MOF coating with high‐quality.