Understanding the role of nickel–iron (oxy)hydroxide (NiFeOOH) electrocatalysts on hematite photoanodes

Abstract

A NiFeOOH electrocatalyst prepared by photo-assisted anodic deposition on hematite performs a dual function: increasing the water oxidation kinetics and suppressing surface charge recombination.

Detection of Spontaneous FeOOH Formation at the Hematite/Ni(Fe)OOH Interface During Photoelectrochemical Water Splitting by Operando X-ray Absorption Spectroscopy

“…As for the ED-hematite, the Ni 25 Fe 75 OOH showed lower OER overpotential than Ni 75 Fe 25 OOH. This is remarkable, given the several reports in the literature on the superior OER performance of Ni 25 Fe 75 OOH. ,, They attributed the lower performance of Ni 75 Fe 25 OOH to the formation of the hematite-NiO x layer at the interface that acts as a recombination center, while Ni 25 Fe 75 OOH effectively collected the photogenerated holes by passivating the hematite surface states. It is important to note here that the Ni 25 Fe 75 OOH consists of two separate phases; a FeOOH phase and a Fe-doped NiOOH phase. , In another study, Kim et al reported a remarkable improvement in the OER performance in BiVO 4 when a FeOOH layer was deposited between the BiVO4 semiconductor and the NiOOH catalyst.…”

“…This is remarkable, given the several reports in the literature on the superior OER performance of Ni 25 Fe 75 OOH. 11,16,27 They attributed the lower performance of Ni 75 Fe 25 OOH to the formation of the hematite-NiO x layer at the interface that acts as a recombination center, while Ni 25 Fe 75 OOH effectively collected the photogenerated holes by passivating the hematite surface states. It is important to note here that the Ni 25 Fe 75 OOH consists of two separate phases; a FeOOH phase and a Fe-doped NiOOH phase.…”

“…10,22−26 Additionally, A third group suggested that NiFeOOH could play both roles. 27 All of these reports highlight the importance of understanding the role of the semiconductor/catalyst interface in dictating the overall performance of the hematite OER performance, which is crucial for future realization of efficient water-splitting photoanodes. 17, 28 Although several characterization studies have been reported on the semiconductor/catalyst interfaces, few of them were focused on the characterization of the combined α-Fe 2 O 3 /NiFeOOH system.…”

“…Moreover, the lack of available experimental tools that can directly investigate interfacial processes is an additional challenge to the semiconductor/catalyst characterization efforts. Several reports suggested that thin films made of NiFeOOH act as direct OER catalysts that play a major role in the process by extracting the photogenerated holes from α-Fe 2 O 3 and utilizing them to drive OER. − Others reported that these overlayers mainly assist hematite in driving OER at lower onset potential by passivating surface defects and slowing the rate of surface recombination, hence reducing the electron-hole recombination probability, which leads to a higher concentration of holes available for OER at the semiconductor surface. ,− Additionally, A third group suggested that NiFeOOH could play both roles . All of these reports highlight the importance of understanding the role of the semiconductor/catalyst interface in dictating the overall performance of the hematite OER performance, which is crucial for future realization of efficient water-splitting photoanodes. , Although several characterization studies have been reported on the semiconductor/catalyst interfaces, few of them were focused on the characterization of the combined α-Fe 2 O 3 /NiFeOOH system.…”

Evaluation of the Efficiency of Photoelectrochemical Activity Enhancement for the Nanostructured LaFeO3 Photocathode by Surface Passivation and Co-Catalyst Deposition

“…A similar study confirmed that catalytic properties of the deposited layer might not be important for the PEC activity of photoanodes, as surface passivation and hence reduced recombination are the predominant sources of PEC activity improvement [ 38 , 39 , 40 ]. It has also been suggested that a co-catalyst can play both a catalytic role and a non-catalytic one, enhancing not only charge transfer but also the overall stability [ 40 , 41 ], while the predominant effect should be dependent on the nature of the photoelectrode material, the nature of the co-catalyst, as well as on the thickness and uniformity of the co-catalyst layer. It is always problematic to deduce the actual role of the co-catalyst, as one needs to address the competition between charge transfer and electron-hole recombination and understand which of these two factors is altered to a greater extent by the co-catalyst deposition [ 40 ].…”