Water Vapor Photoelectrolysis in a Solid-State Photoelectrochemical Cell with TiO₂ Nanotubes Loaded with CdS and CdSe Nanoparticles

Abstract

In this study, polyol-made CdS and CdSe crystalline nanoparticles (NPs) are loaded by impregnation on TiO 2 nanotube arrays (TNTAs) for solar-simulated light-driven photoelectrochemical (PEC) water vapor splitting. For the first time, we introduce a safe way to utilize toxic, yet efficient photocatalysts by integration in solid-state PEC (SSPEC) cells. The enabling features of SSPEC cells are the surface protonic conduction mechanism on TiO 2 and the use of polymeric electrolytes, such as Nafion instead of liquid ones, for operation with gaseous reactants, like water vapor from ambient humidity. Herein, we studied the effects of both the operating conditions in gaseous ambient atmospheres and the surface modifications of TNTAs-based photoanodes with well-crystallized CdS and CdSe NPs. We showed 3.6 and 2.5 times increase in the photocurrent density of defective TNTAs modified with CdS and CdSe, respectively, compared to the pristine TNTAs. Electrochemical impedance spectroscopy and structural characterizations attributed the improved performance to the higher conductivity induced by intrinsic defects as well as to the enhanced electron/hole separation at the TiO 2 /CdS heterojunction under gaseous operating conditions. The SSPEC cells were evaluated by cycling between high relative humidity (RH) (80%) and low RH levels (40%), providing direct evidence of the effect of RH and, in turn, adsorbed water, on the cell performance. Online mass spectrometry indicated the corresponding difference in the H 2 production rate. In addition, a complete restoration of the SSPEC cell performance from low to high RH levels was also achieved. The presented system can be employed in off-grid, water depleted, and air-polluted areas for the production of hydrogen from renewable energy and provides a solution for the safe use of toxic, yet efficient photocatalysts.

Basic comprehension and recent trends in photoelectrocatalytic systems

“…3A), at room temperature both in the liquid-phase [83][84][85][86] and the gasphase (i.e., with humidified carrier gas). [86][87][88] In most cases TiO 2based photoanodes were employed, like P25 85 or titania nanotube arrays (TNTAs), typically prepared by the electrochemical anodization of titanium, 84,86 and in some cases doped with CdS 83,87 or CdSe. 87 Among all of them, the highest photocurrent density was obtained by Li et al with TNTAs after calcination at 450 °C (Fig.…”

“…There are some studies in the literature using PEC cells with a membrane configuration (Conf. 1), [83][84][85][86][87][88][89][90] mainly for water splitting. A PEM PEC setup is typically composed of (i) a translucent glass such as Pyrex® or quartz to allow visible and/or UV-light illumination to irradiate the photoelectrode; (ii) chemically inert joints made of polymer materials such as Teflon® to separate the two modular half-cells; (iii) O-rings to seal the window; (iv) metal-based connectors to link the electrodes to a potentiostat-galvanostat (Fig.…”

Scaling up BiVO4 Photoanodes on Porous Ti Transport Layers for Solar Hydrogen Production

“…[23,24,33] This approach creates a new challenge, namely the development of techniques to deposit photoabsorber coatings onto porous substrates. Although there have been demonstrations of such approaches [33][34][35][36][37][38][39][40] the majority of the studies are limited to either low surface area (~1 cm 2 ) or low-performing photoelectrodes (< 1 mA • cm À 2 @ 1.23 V vs RHE). [41][42][43] Additionally, the concept of the use of co-catalysts, which has been shown to significantly enhance thin film photoelectrode performance, has not been effectively implemented in the porous substrate photoelectrode design.…”

In situ Cu single atoms anchoring on MOF-derived porous TiO2 for the efficient separation of photon-generated carriers and photocatalytic H2 evolution

“…Compared with electrocatalytic hydrogen production, photocatalytic water splitting for hydrogen production has the advantages of low cost, safety and environmental friendliness, which has attracted extensive attention recently. [1][2][3] Different ways and means have been invented to modify the base semiconductors for a higher activity, selectivity and stability in the hydrogen evolution reaction, such as element doping, 4,5 semiconductor coupling, [6][7][8] supported single atom, etc. Thereinto, single atom catalysts (SACs) have rapidly advanced over the last several years, and consist of stable isolated metal atoms supported on suitable substrates.…”