Cobalt-Doped ZnO Nanorods Coated with Nanoscale Metal–Organic Framework Shells for Water-Splitting Photoanodes

Abstract

Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal–organic framework (MOF). The light absorption of the ZnO NRs is engineered toward the visible region by Co-doping, while the MOF significantly improves the stability and charge separation and transfer properties of the NRs. This synergetic combination of doping and nanoscale surface functionalization boosts the current density and functional lifetime of the photoanodes while achieving an unprecedented incident photon to current efficiency (IPCE) of 75% at 350 nm, which is over 2 times that of pristine ZnO. A theoretical model and band structure for the core–shell nanostructure is provided, highlighting how this nanomaterial combination provides an attractive pathway for the design of robust and highly efficient semiconductor-based photoanodes that can be translated to other semiconducting oxide systems.

Optical properties and carrier dynamics in Co-doped ZnO nanorods

“…S1, ESI † ) clearly shows the rather homogeneous distribution of Co along the ZnO NR, in line with observations from our previous work. 25 As it will be clear in the following, the optical properties of the samples change according to the increase in the nominal Co content. Hence, in line with literature, 29 we will compare the influence that different nominal values of Co 2+ in growth solution have on the optoelectronic properties of the ZnO NRs.…”

“…While this paper focuses on the optical properties and carrier dynamics in Co-doped ZnO NRs, it has been demonstrated, in a complementary study that combining ZnO NRs and Co-doping in conjunction with a transparent functionalization of metal–organic framework leads to a more efficient photoelectrochemical cell. 25 …”

Metal–Organic Framework-Derived Co-Doped ZnO Nanostructures Anchored on N-Doped Carbon as a Room-Temperature Chemiresistive Hydrogen Sensor

“…For instance, ZIF-8 is used as a template for different ZnO nanostructureshollow ZnO, ZnO nanowires, ZnO nanorods, and so on. , Bimetallic ZIFs were also used to dope other metal ions in ZnO nanomaterials with high dispersion. ZnO properties can be greatly improvised by doping with other metals such as Co. − Due to its similar ionic radius and divalent state, remarkable improvement in the electronic structure has been observed even when smaller amounts of Co (<2 wt %) are doped in ZnO nanomaterials. − …”

Semi-conducting Ni/Zn nano-hybrids’ driven efficient electro-catalytic performance: fabrication, characterization, and electrochemical features’ elucidation

“…Such an enhanced performance is attributive of the improvement in the light absorption brought in ZnO nanorods via Co doping. In addition to this, molecular organic framework improved the transferal aspects, stability, and separation of the charged species (35). Similarly, doping of ZnO with Fe synthesized via aerosol-assisted chemical vapor deposition (AACVD) has also been reported to be effective in water splitting (36).…”