Bandar AlOtaibi

Highly Stable Photoelectrochemical Water Splitting and Hydrogen Generation Using a Double-Band InGaN/GaN Core/Shell Nanowire Photoanode

We report on the first demonstration of stable photoelectrochemical water splitting and hydrogen generation on a double-band photoanode in acidic solution (hydrogen bromide), which is achieved by InGaN/GaN core/shell nanowire arrays grown on Si substrate using catalyst-free molecular beam epitaxy. The nanowires are doped n-type using Si to reduce the surface depletion region and increase current conduction. Relatively high incident-photon-to-current-conversion efficiency (up to ~27%) is measured under ultraviolet and visible light irradiation. Under simulated sunlight illumination, steady evolution of molecular hydrogen is further demonstrated.

High Efficiency Solar-to-Hydrogen Conversion on a Monolithically Integrated InGaN/GaN/Si Adaptive Tunnel Junction Photocathode

H2 generation under sunlight offers great potential for a sustainable fuel production system. To achieve high efficiency solar-to-hydrogen conversion, multijunction photoelectrodes have been commonly employed to absorb a large portion of the solar spectrum and to provide energetic charge carriers for water splitting. However, the design and performance of such tandem devices has been fundamentally limited by the current matching between various absorbing layers. Here, by exploiting the lateral carrier extraction scheme of one-dimensional nanowire structures, we have demonstrated that a dual absorber photocathode, consisting of p-InGaN/tunnel junction/n-GaN nanowire arrays and a Si solar cell wafer, can operate efficiently without the strict current matching requirement. The monolithically integrated photocathode exhibits an applied bias photon-to-current efficiency of 8.7% at a potential of 0.33 V versus normal hydrogen electrode and nearly unity Faradaic efficiency for H2 generation. Such an adaptive multijunction architecture can surpass the design and performance restrictions of conventional tandem photoelectrodes.

A Metal-Nitride Nanowire Dual-Photoelectrode Device for Unassisted Solar-to-Hydrogen Conversion under Parallel Illumination

A dual-photoelectrode device, consisting of a photoanode and photocathode with complementary energy bandgaps, has long been perceived as an ideal scheme for achieving high efficiency, unassisted solar-driven water splitting. Previously reported 2-photon tandem devices, however, generally exhibit an extremely low efficiency (<0.1%), which has been largely limited by the incompatibility between the two photoelectrode materials. Here we show that the use of metal-nitride nanowire photoelectrodes, together with the scheme of parallel illumination by splitting the solar spectrum spatially and spectrally, can break the efficiency bottleneck of conventional 2-photon tandem devices. We have first investigated a dual-photoelectrode device consisting of a GaN nanowire photoanode and an InGaN nanowire photocathode, which exhibited an open circuit potential of 1.3 V and nearly 20-fold enhancement in the power conversion efficiency under visible light illumination (400-600 nm), compared to the individual photoelectrodes in 1 mol/L HBr. We have further demonstrated a dual-photoelectrode device consisting of parallel-connected metal-nitride nanowire photoanodes and a Si/InGaN nanowire photocathode, which can perform unassisted, direct solar-to-hydrogen conversion. A power conversion efficiency of 2% was measured under AM1.5G 1 sun illumination.

Near-infrared colloidal quantum dots for efficient and durable photoelectrochemical solar-driven hydrogen production

A new hybrid photoelectrochemical photoanode is developed to generate H2 from water. The anode is composed of a TiO2 mesoporous frame functionalized by colloidal core@shell quantum dots (QDs) followed by CdS and ZnS capping layers. Saturated photocurrent density as high as 11.2 mA cm−2 in a solar‐cell‐driven photoelectrochemical system using near‐infrared QDs is obtained.

Epitaxial Bi2FeCrO6 Multiferroic Thin Film as a New Visible Light Absorbing Photocathode Material

Ferroelectric materials have been studied increasingly for solar energy conversion technologies due to the efficient charge separation driven by the polarization induced internal electric field. However, their insufficient conversion efficiency is still a major challenge. Here, a photocathode material of epitaxial double perovskite Bi(2) FeCrO(6) multiferroic thin film is reported with a suitable conduction band position and small bandgap (1.9-2.1 eV), for visible-light-driven reduction of water to hydrogen. Photoelectrochemical measurements show that the highest photocurrent density up to -1.02 mA cm(-2) at a potential of -0.97 V versus reversible hydrogen electrode is obtained in p-type Bi(2) FeCrO(6) thin film photocathode grown on SrTiO(3) substrate under AM 1.5G simulated sunlight. In addition, a twofold enhancement of photocurrent density is obtained after negatively poling the Bi(2) FeCrO(6) thin film, as a result of modulation of the band structure by suitable control of the internal electric field gradient originating from the ferroelectric polarization in the Bi(2) FeCrO(6) films. The findings validate the use of multiferroic Bi(2) FeCrO(6) thin films as photocathode materials, and also prove that the manipulation of internal fields through polarization in ferroelectric materials is a promising strategy for the design of improved photoelectrodes and smart devices for solar energy conversion.

A Monolithically Integrated Gallium Nitride Nanowire/Silicon Solar Cell Photocathode for Selective Carbon Dioxide Reduction to Methane

A gallium nitride nanowire/silicon solar cell photocathode for the photoreduction of carbon dioxide (CO2 ) is demonstrated. Such a monolithically integrated nanowire/solar cell photocathode offers several unique advantages, including the absorption of a large part of the solar spectrum and highly efficient carrier extraction. With the incorporation of copper as the co-catalyst, the devices exhibit a Faradaic efficiency of about 19 % for the 8e(-) photoreduction to CH4 at -1.4 V vs Ag/AgCl, a value that is more than thirty times higher than that for the 2e(-) reduced CO (ca. 0.6 %).

Photoelectrochemical reduction of carbon dioxide using Ge doped GaN nanowire photoanodes

We report on the direct conversion of carbon dioxide (CO2) in a photoelectrochemical cell consisting of germanium doped gallium nitride nanowire anode and copper (Cu) cathode. Various products including methane (CH4), carbon monoxide (CO), and formic acid (HCOOH) were observed under light illumination. A Faradaic efficiency of ∼10% was measured for HCOOH. Furthermore, this photoelectrochemical system showed enhanced stability for 6 h CO2 reduction reaction on low cost, large area Si substrates.