Yiping Hu

Facile regrowth of Mg-Fe2O3/P-Fe2O3 homojunction photoelectrode for efficient solar water oxidation

The photoelectrochemical (PEC) water splitting performance of hematite-based photoanodes is still far from their theoretical value due to the ultrafast charge recombination in bulk and on the surface. In response, we developed a regrowth strategy to fabricate a photoanode with metallic Mg-doped α-Fe2O3 coating on nonmetallic P-doped α-Fe2O3 nanorods (Mg-Fe2O3/P-Fe2O3 NRs). This homojunction structure fulfils the requirements of both high charge separation efficiency and favorable band alignment, showing a high photocurrent density (4.7-fold higher than pristine Fe2O3) and low onset potential of 0.68 VRHE. Experimental and density functional theory (DFT) results reveal that the origin of such superior PEC performance is P-doping and Mg-Fe2O3 coating, which efficiently eliminate lattice mismatching, improve the conductivity of hematite, and simultaneously promote the photogenic carriers separation by the built-in electric field. This promising design may open an avenue to fabricating various efficient homojunction photoanodes for practical PEC water splitting.

Ultrafine CoPS nanoparticles encapsulated in N, P, and S tri-doped porous carbon as an efficient bifunctional water splitting electrocatalyst in both acid and alkaline solutions

Searching for highly efficient, stable and non-noble metal electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is crucial to renewable-energy conversion systems. Cobalt phosphosulfide (CoPS) is regarded as a promising electrocatalyst for the HER in acid solution. Nonetheless, there are no studies of its HER and OER activity in basic solution. Herein, we engineer a novel and highly efficient water splitting electrocatalyst of ultrafine CoPS nanoparticles (NPs) encapsulated in N, P, and S tri-doped porous carbon (CoPS@NPS-C) through metal–organic frameworks (MOFs) and commercial carbon black (XC-72) as precursors. The abundant and evenly distributed metals of MOFs form ultrafine CoPS NPs, and the rich N organic ligands of MOFs and XC-72 are shaped into the NPS-C to protect CoPS NPs leading to long-term stability in water-splitting applications. Meanwhile, the strong interaction between CoPS and NPS-C in this special structure not only ensures the high activity of the HER in acid solution and the OER in alkaline solution, but also maintains good HER performance in alkaline solution. The results display that the novel structure electrocatalyst of CoPS@NPS-C has great potential in water-splitting applications.

NiO Nanoparticles Anchored on Phosphorus-Doped α-Fe2O3 Nanoarrays: An Efficient Hole Extraction p-n Heterojunction Photoanode for Water Oxidation

The photoelectrochemical (PEC) water-splitting efficiency of a hematite-based photoanode is still far from the theoretical value due to its poor surface reaction kinetics and high density of surface trapping states. To solve these drawbacks, a photoanode consisting of NiO nanoparticles anchored on a gradient phosphorus-doped α-Fe2 O3 nanorod (NR) array (NiO/P-α-Fe2 O3 ) was fabricated to achieve optimal light absorption and charge separation, as well as rapid surface reaction kinetics. Specifically, a photoanode with the NR array structure allowed a high mass-transport rate to be achieved, while phosphorus doping effectively decreased the number of surface trapping sites and improved the electrical conductivity of α-Fe2 O3 . Furthermore, the p-n junction that forms between NiO and P-α-Fe2 O3 can further improve the PEC performance due to efficient hole extraction and the water oxidization catalytic activity of NiO. Consequently, the NiO/P-α-Fe2 O3 NR photoanode produced a high photocurrent density of 2.08u2005mAu2009cm-2 at 1.23u2005V versus a reversible hydrogen electrode and a 110u2005mV cathodic shift of the onset potential. This rational design of structure offers a new perspective in exploring high-performance PEC photoanodes.

Dual Modification of a BiVO4 Photoanode for Enhanced Photoelectrochemical Performance

Bismuth vanadate (BiVO4 ) has triggered extensive interest in photoelectrochemical (PEC) water splitting, owing to its narrow band gap and sufficiently positive valence band. However, some defects still exist to block the solar utilization efficiency and hydrogen evolution kinetics. Herein, the NiMoO4 semiconductor is combined with a BiVO4 photoanode, for the first time, and excellent PEC performance is achieved on the basis of heterojunction formation and favorable conductivity of NiMoO4 . In addition, it has been demonstrated that NiMoO4 promotes the light absorption ability, charge separation efficiency, and surface charge-transfer efficiency comprehensively. To further improve the photoconversion efficiency, cobalt phosphate, as an oxygen evolution reaction cocatalyst, is deposited on the above electrode and achieves a much enhanced utilization efficiency of 1.18u2009%, with a photocurrent density of 5.3u2005mAu2009cm-2 at 1.23u2005V versus a reversible hydrogen electrode; this exceeds most results reported to date. This rational and unique photoanode construction provides a new thread for the photoelectrode designation.

Heterojunction and Oxygen Vacancy Modification Strategies of ZnO Nanorod Arrays Photoanode for Enhanced Photoelectrochemical Water Splitting

Application of ZnO in the field of photoelectrochemical water splitting is limited because of its wide-band-gap and high recombination rate. Herein is reported the design of an efficient ZnO photoanode deposited with CoOx nanoparticles to achieve a heterojunction and oxygen vacancies. The CoOx nanoparticles with abundant oxygen vacancies were anchored onto the nanorod arrays by spin coating and calcination followed by a solvothermal treatment. CoOx nanoparticles serve the dual function of forming a p-n heterojunction to facilitate the separation of photogenerated carriers, and act as a cocatalyst to decrease water oxidation barrier. Finally, oxygen vacancies increase the number of active redox sites and act as hole traps, enabling their migration to the electrode/electrolyte interface. The composite photoanode exhibits a high incident photon-to-current conversion efficiency (76.7u2009% at 350u2005nm), which is twice that of pristine ZnO, and a photoconversion efficiency of 0.68u2009% (0.73u2005V versus RHE). The current approach can be expanded to fabricate other efficient photocatalysts.