Nanomaterials for photoelectrochemical water splitting - review

A technical and environmental comparison between hydrogen and some fossil fuels

BiVO4 is a considerably promising semiconductor for photoelectrochemical water splitting due to its stability, low cost and moderate band gap. In this research, g-C3N4 was proposed in Z-scheme configuration which boosted the performance of BiVO4 up to four times. The experimental observations were counterchecked with Density Functional Theory (DFT) simulations. A TiO2/BiVO4 heterojunction was developed and its performance was compared with that of g-C3N4/BiVO4. The photocurrent for g-C3N4/BiVO4 was 0.42 mAcm−2 at 1.23 V vs. RHE which was the highest among g-C3N4 based Z-scheme heterojunction devices. Lower charge transfer resistance, higher light absorption and more oxygen vacancy sites were observed for the g-C3N4 based heterojunction. The simulated results attested that g-C3N4 and BiVO4 formed a van der Waals type heterojunction, where an internal electric ﬁeld facilitated the separation of electron/hole pair at g-C3N4/BiVO4 interface which further restrained the carrier recombination. Both the valence and conduction band edge positions of g-C3N4 and BiVO4 changed with the Fermi energy level. The resulted heterojunction had small effective masses of electrons (0.01 me) and holes (0.10 me) with ideal band edge positions where both CBM and VBM were well above and below the redox potential of water.

Enhanced photoelectrochemical performance of Z-scheme g-C3N4/BiVO4 photocatalyst

A review on NiFe-based electrocatalysts for efficient alkaline oxygen evolution reaction

Hydrogen produced from low-emission primary energy sources, particularly renewable energy, is a potential alternative transport fuel to gasoline and diesel that can contribute to reducing greenhouse gas emissions and improving global energy security. Hydrogen fuelling stations are one of the most important parts of the distribution infrastructure required to support the operation of hydrogen fuel cell electric vehicles and hydrogen internal combustion engine vehicles. If there is to be substantial market penetration of hydrogen vehicles in the transport sector, the introduction of commercial hydrogen vehicles and the network of fuelling stations to supply them with hydrogen must take place simultaneously. The present paper thus reviews the current state of the art and deployment of hydrogen fuelling stations. It is found that by 2013, there were 224 working hydrogen stations distributed over 28 countries. Some 43% of these stations were located in North and South America, 34% in Europe, 23% in Asia, and none in Australia. The state of the art in the range of hydrogen production processes is briefly reviewed. The importance of producing hydrogen using renewable energy sources is emphasised for a transition to hydrogen fuel cell vehicles to contribute to greenhouse gas emission reduction targets. 2.3–5.8/H2kg for SMR A classification of hydrogen refuelling stations is introduced, based on the primary energy source used to produce the hydrogen, the production process, and whether the hydrogen is made on site or delivered to the site. The current state of deployment of hydrogen fuelling stations in each major region of the world is then reviewed in detail. The costs of producing hydrogen vary from $1.8 to 2.9/H2 kg for Coal gasification, 2.3–5.8/H2 kg for SMR, $6–7.4/H2 kg for wind power and $6.3–25.4/H2 kg depending on the cost of the PV system. The lowest cost of hydrogen is nearing competitiveness with petroleum fuels. Finally conclusions are drawn about the progress to date in establishing this crucial component of the infrastructure to enable hydrogen-powered vehicles to become a commercial reality.

Automotive hydrogen fuelling stations: An international review

Cobalt-Phosphate modified TiO2/BiVO4 nanoarrays photoanode for efficient water splitting

Bifunctional Ni1−xFex layered double hydroxides/Ni foam electrodes for high-efficient overall water splitting: A study on compositional tuning and valence state evolution

Surface treated TiO2 nanorod arrays for the improvement of water splitting

Photovoltaic devices in hydrogen production

A novel structure of TiO2 films has been successfully prepared on a fluorine-doped tin oxide (FTO) glass substrate through a feasible two-step hydrothermal method. In the first-step hydrothermal growth results in one-dimensional (1D) rutile TiO2 nanorod arrays capped by 3 dimensional (3D) rutile TiO2 nanorods, and in the second-step hydrothermal etching in hydrochloric acid solution leads to the selective etching of 3D TiO2 nanorods to form 3D nanotubes at first, and then the tip wall of the nanotubes divide into secondary nanowires with reduced diameters. The resultant bi-layer TiO2 network structure films were used as photoanodes in dye-sensitized solar cells (DSSCs). The 3D rutile network structure provides a large surface area for dye-loading and the oriented nanorod arrays at the bottom layer enable a direct pathway for electron transport. The influence of etching time toward the photovoltaic performance of the DSSCs fabricated from TiO2 network structure films has been comprehensively studied. It was found that the amount and the length of the secondary nanowires reached a maximum when the etching time was 14 h, which resulted in the largest surface area and best dye-loading ability of the TiO2 network structure films, producing an overwhelming power conversion efficiency (PCE) of 5.71%. In addition, TiCl4 post-treatment was employed to further improve the PCE. Through optimizing the amount of the titanium precursor and the time of TiCl4 treatment, the DSSCs assembled with a TiO2 1D/3D network structure photoanode presented a markedly enhanced efficiency of 7.68%, when the TiO2 films were synthesized with 0.9 ml tetrabutyl titanate followed by 12 h etching and treated with TiCl4 for 48 h.

Qingyun Liu

Papers

Cobalt-Phosphate modified TiO2/BiVO4 nanoarrays photoanode for efficient water splitting

Bifunctional Ni1−xFex layered double hydroxides/Ni foam electrodes for high-efficient overall water splitting: A study on compositional tuning and valence state evolution

Surface treated TiO2 nanorod arrays for the improvement of water splitting

Photovoltaic devices in hydrogen production

Optimizing the prepared condition of TiO2 1D/3D network structure films to enhance the efficiency of dye-sensitized solar cells