Metal–Organic Framework Derived Co₃O₄/TiO₂/Si Heterostructured Nanorod Array Photoanodes for Efficient Photoelectrochemical Water Oxidation

Abstract

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. 1002/adfm.201701102. photoexcitation of semiconductor photoanode; the separation and migration of photoinduced carriers; the surface water reduction on the cathode; and water oxidation on the photoanode with photoinduced electrons/holes. [8][9][10] Therefore, to achieve effective solar-to-hydrogen (STH) process, all steps stated above should be in very efficient progress, which requires high optical response for the photoanode materials, [11] efficient carrier separation, and surface reaction. [12,13] Metal oxides (MOs), such as TiO 2 , [14] α-Fe 2 O 3 , [15] and WO 3 , [16,17] have been widely investigated as the photoanode materials for PEC water splitting, for their low-cost, environmentfriendly properties. However, as intrinsic semiconductor, the PEC performance of pristine MO photoanode is always hindered by the poor carrier mobility, narrow optical-response range, and slow surface water oxidation kinetics. [18,19] Therefore, designing composited photoanodes with proper band-gap energy structure is considered to be a promising route to overcome these limitations induced poor PEC performance. [20][21][22] For instance, via constructing semiconductor heterojunction with matched band position, the separation and transportation of photoinduced carrier can be effectively enhanced (such as Bi 2 MoO 6 /Si, [23] Ag/Fe 2 O 3 , [24] NiFe-LDH/C 3 N 4[25] heterojunction). Particularly, benefiting from the outstanding visiblelight response performance and carrier mobility within silicon, it has long been regarded as the most suitable material to build the solar energy conversion device. [26] As the conduction band (CB) of silicon is more negative than most of the common MO semiconductors (e.g., TiO 2 , [27,28] WO 3 ), [29] silicon can bring better electron reduction kinetics on the counter electrode. [30] However, it is not efficient to directly use only silicon as anode for PEC water oxidation due to the valence band (VB) of silicon is higher than the water oxidation potential. [23,31] In this regard, constructing MO/Si heterostructured photoanode is proposed to overcome the potential shortcomings of both MO and silicon simultaneously. To further improve the surface water oxidation kinetics of photoanode, introducing oxygen evolution reaction (OER) cocatalysts is regarded as a promising way to accelerate the four-electron water oxidation kinetics during the water splitting process. [8,32,33] Recently, the outstanding OER performance Water Splitting

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

“…[ 141] The prepared photoanode shows fair stability and achieves a photocurrent density of 2.71 mA cm −2 at 1.23 V RHE in alkaline electrolyte on account of the large specific surface area and enriched pore structure originated from MOFs. NiO x : Nickel oxide (NiO x ) is viewed as one of the best OER cocatalysts as it is earth-abundant, cost-efficient, stable even at high pH, and optically transparent under visible light, which enable the deposited photoanodes possess high durability and excellent water oxidation performance.…”

“…Very lately, Tang et al [141] fabricated the Co 3 O 4 cocatalyst derived from MOFs and incorporated it with TiO 2 /Si heterojunction. MOFs, which have characteristics of large porosity and high surface area, are usually applied in electrocatalysis, while they are hardly utilized as PEC water oxidation cocatalysts before.…”

Metal–Organic Framework Derived Narrow Bandgap Cobalt Carbide Sensitized Titanium Dioxide Nanocage for Superior Photo‐Electrochemical Water Oxidation Performance

“…Solar energy conversion has been regarded as one of the most promising strategies to alleviate global energy crisis caused by the depletion of fossil fuels, among which, photo‐electrochemical (PEC) water splitting has attracted considerable attention for its direct conversion from solar energy to chemical energy . Since Fujishima reported pioneer work on water splitting, TiO 2 has been widely investigated as the ideal candidate for photoanode materials for PEC water splitting owing to its suitable band position, facile fabricating method, and eco‐friendly features . However, the PEC water splitting performance of pristine TiO 2 photoanodes still remains unsatisfied owing to its poor photogenerated carrier separation efficiency, insufficient light response, and sluggish surface water oxidation kinetics .…”

Rational Microstructure Design on Metal–Organic Framework Composites for Better Electrochemical Performances: Design Principle, Synthetic Strategy, and Promotion Mechanism

“…By first engineering Co(OH) 2 seeds on the surface of TiO 2 nanorod arrays on Si substrate through an electrochemical deposition method, the Si/TiO 2 /Co(OH) 2 was then reacted with 2‐methylimidazole under 80 °C to convert Co(OH) 2 into Zif‐67 crystals due to the slowly dissolving of Co(OH) 2 in 2‐methylimidazole containing solutions. The obtained Si/TiO 2 /Zif‐67 nanorod arrays can be transformed into Si/TiO 2 /Co 3 O 4 and Si/TiO 2 /CoP‐CN, respectively, exhibiting excellent performance for photoelectrochemical water splitting . For instance, Si/TiO 2 /Co 3 O 4 can display a photoconversion efficiency of 0.54% (1.04 V vs RHE) and photocurrent density of 2.71 mA cm −2 in alkaline electrolyte.…”

“…The obtained Si/TiO 2 /Zif-67 nanorod arrays can be transformed into Si/TiO 2 /Co 3 O 4 and Si/ TiO 2 /CoP-CN, respectively, exhibiting excellent performance for photoelectrochemical water splitting. [134,135] For instance, Si/ TiO 2 /Co 3 O 4 can display a photoconversion efficiency of 0.54% (1.04 V vs RHE) and photocurrent density of 2.71 mA cm −2 in alkaline electrolyte. Zif-67 nanosheets can also be engineered on the surface of TiO 2 octahedrons, which were then converted into Co 3 C under high-temperature treatment in argon.…”