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The well-designed FeCo-MOF/Fe 2 O 3 compound photoanode displays favorable PEC performances, which can be attributed to the coating of multifunctional FeCo MOF nanolayer that passivate the surface states, construct the p-n heterojunction and improve the water oxidation kinetics, all of these enable the substantially promoted charge separation and transport. [Display omitted] • Ultrathin FeCo MOF nanolayers coated on Fe 2 O 3 photoanode are in-situ formed. • Multifunctional roles of FeCo MOF on Fe 2 O 3 is disclosed. • This design endows photoanode with boosted charge separation/injection efficiency. • The catalytic mechanism for PEC water oxidation is unravelled. Owing to the high theoretical photocurrent density, the hematite (α -Fe 2 O 3) based photoanode has been intensively concerned in photoelectrochemical (PEC) water splitting, but its serious charge recombination and sluggish water oxidation kinetics are still the stumbling blocks. This work reports a high-performance Fe 2 O 3 -based photoanode achieved by coating multifunctional FeCo-bimetal organic framework (MOF) nanolayers (NLs) on Fe 2 O 3 nanoarrays via an in-situ solvothermal process. The FeCo MOF NLs introduced not only effectively passivate the surface states of Fe 2 O 3 photoanode and boost the water oxidation kinetics serving as the cocatalyst, but also construct p-n heterojunctions with Fe 2 O 3 to accelerate the directional migration and separation of photogenerated charge carriers. Expectedly, the as-obtained FeCo-MOF/Fe 2 O 3 photoanode exhibits an apparent negative shift of onset potential, an excellent long-term PEC stability, and highly improved photocurrent density. This finding provides a novel and effective strategy to introduce advanced multifunctional surface coating for enhancing the PEC performance of photoelectrodes. [ABSTRACT FROM AUTHOR]

The well-designed MoO 3- x /Fe 2 O 3- x photoanode exhibits superior PEC water oxidation performance due to the efficient charge separation and transport derived from the introduced MoO 3 surface passivation layer and oxygen vacancy. • Establishing passivation effect of MoO 3 on Fe 2 O 3 photoanode. • Collaboration of passivation layer and oxygen vacancy on Fe 2 O 3 was designed. • The boosted charge separation and transport are achieved on modified photoanode. • Exhibiting superior water oxidation performance on MoO 3- x /Fe 2 O 3- x photoanode. To seek effective strategies that improve the photoelectrochemical water oxidation performance of hematite (α -Fe 2 O 3) photoanodes is still challenging owning to their abundant surface states and low charge transfer efficiency. Herein, a facile impregnation method with an annealing process was developed to synthesize MoO 3 modified Fe 2 O 3 photoanodes using the MoO 3 layer as an effective passivation component to decrease surface states and thus to improve the charge separation and transfer process at the electrode/electrolyte interfaces. The oxygen vacancies were subsequently introduced to steer the electrical conductivity, and further to boost the charge separation and transfer. The optimized MoO 3- x /Fe 2 O 3- x photoanode displays a photocurrent density of 2.6 mA cm–2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G irradiation, 2.2 times that of the Fe 2 O 3 (1.2 mA cm–2). The synergetic integration of passivation layer and oxygen vacancies on photoelectrodes heralds an efficient paradigm for solar energy conversion. [ABSTRACT FROM AUTHOR]