Solar-to-hydrogen Efficiency Research Articles

Fabrication of a Monolithic Heterostructured c-Si/BiVO4 Core-Shell Photoanode for Unassisted Solar Water Splitting

Photoelectrochemical (PEC) water splitting is a promising way of storing solar energy in hydrogen, which can be used as a carbon-free fuel or a chemical feed stock. A tandem-junction PEC device offers a high theoretical solar-to-hydrogen (STH) efficiency due to the additive voltages across two photoabsorbers and the better utilization of the solar spectrum. Modeling STH efficiency as a function of band gap for a tandem device shows that over 20% STH can be achieved with band gaps of 1.2 and 1.8 eV.1 One promising photoabsorber material combination is c-Si paired with a metal oxide, especially BiVO4. In addition to the appropriate band structure alignment of both semiconductors, c-Si and BiVO4 are low cost, earth abundant, and industrially scalable. However, the key challenges for these materials are the instability of c-Si in aqueous environment and the poor electronic properties of BiVO4, a common limitation for most metal oxides. Hence, only a very few c-Si/metal oxide systems have been demonstrated for unassisted water splitting.2 In this work, we present the fabrication of a monolithic heterostructured c-Si/BiVO4 core-shell tandem based monolithic device capable of performing spontaneous water splitting without any precious metal. The wafer scaled device architecture was prepared by (1) nanostructuring of the d c-Si substrate to serve as both a bottom absorber and a scaffold to improve the charge separation of BiVO4; (2) tuning the c-Si p-n junction depth to maximize the device photovoltage; (3) engineering the SnO2 interfacial layer to passivate the c-Si/BiVO4 interface and protect the c-Si p-n junction; (4) conformally coating a BiVO4 thin film on the nanostructured Si; and (5) decorating the c-Si and BiVO4surfaces with both oxygen and a hydrogen evolution catalysts. (1) Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2014, 7(5), 1372-1385. (2) (a) Shaner, M. R.; Fountaine, K. T.; Ardo, S.; Coridan, R. H.; Atwater, H. A.; Lewis, N. S. Energy Environ. Sci. 2014, 7 (2), 779-790; (b) Liu, C.; Tang, J.; Chen, H. M.; Liu, B.; Yang, P. Nano Lett. 2013, 13 (6), 2989-2992; (c) Xu, P.; Feng, J.; Fang, T.; Zhao, X.; Li, Z.; Zou, Z. RSC Adv. 2016, 6 (12), 9905-9910.

Molybdenum Disulfide As a Protection Layer and Catalyst for Gallium Indium Phosphide Solar Water Splitting Photocathodes

Gallium indium phosphide (GaInP2) is a semiconductor with a nearly ideal bandgap for solar water-splitting as the top absorber in a dual junction tandem absorber device. It has been used in conjunction with a gallium arsenide (GaAs) bottom absorber in an overall water splitting cell with 12.4% solar-to-hydrogen (STH) efficiency, one of the highest STH efficiencies for an integrated photoelectrochemical (PEC) water-splitting device reported to date. However, GaInP2 suffers from one of the biggest challenges facing the field: instability due to electrochemical corrosion in aqueous electrolytes. Molybdenum disulfide (MoS2) nanomaterials can be used to both protect GaInP2 and significantly improve its catalytic ability since it is resistant to corrosion and also possesses high activity for the hydrogen evolution reaction (HER). In this work, we demonstrate that GaInP2 photocathodes coated with thin MoS2 surface protecting layers exhibit excellent activity and stability for solar hydrogen production and we probe the details of failure mechanisms using novel flow cell microscopic and spectroscopic techniques. Our GaInP2 photocathodes demonstrated no loss in performance (photocurrent onset potential, fill factor, and light limited current density) until 60 hours of operation which represents a five-hundred fold increase in stability compared to bare p-GaInP2 samples tested in identical conditions. We believe this to be one of the first successful attempts to stabilize GaInP2 using a thin film protection layer scheme. Furthermore, as this protection scheme has previously been used successfully on silicon photocathodes, this work highlights the potential for MoS2 to be used as a thin film protection layer for many different semiconductor water splitting devices that are unstable in acid. Using a custom-designed flow cell coupled with various microscopic and spectroscopic techniques (optical, Raman, FT-IR), we gained a greater understanding of the failure mechanisms of MoS2 as a thin-film protection layer. We discovered that pinhole formation in the MoS2 layer exposes the GaInP2 substrate, which readily corrodes in the acidic conditions, ultimately leading to device degradation. The flow cell further allowed us to capture the time scale of this pinhole formation. These insights represent a deeper understanding of MoS2 as a protection layer and can be leveraged to improve the stability of thin film protected semiconductor water splitting devices. References Khaselev, O.; Turner, J. A., A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production Via Water Splitting. Science 1998, 280, 425-427. Benck, J. D.; Lee, S. C.; Fong, K. D.; Kibsgaard, J.; Sinclair, R.; Jaramillo, T. F., Designing Active and Stable Silicon Photocathodes for Solar Hydrogen Production Using Molybdenum Sulfide Nanomaterials. Advanced Energy Materials 2014, 4, 1-8 Britto R.J., Benck J.D., Young J.L., Hahn C., Deutsch, T.G., Jaramillo T.F. In Review (2016) Figure 1

Solar-to-Hydrogen Efficiency: Shining Light on Photoelectrochemical Device Performance

Direct photoelectrochemical (PEC) hydrogen production aims to provide a clean and cost-effective solar fuel. Solar-to-hydrogen (STH) conversion efficiency is central to evaluating and comparing research results, and it largely establishes the prospect for successfully introducing commercial solar water-splitting systems. Present measurement practices do not follow well-defined standards, and common methods potentially impact research results and their implications. We demonstrate underestimated influence factors and experimental strategies for improved accuracy[1]. Our focus is tandem devices that have the prospect for greater STH efficiency[2], but increased complexity that requires more careful consideration of characterization practices. We perform measurements on an advanced version of the classical GaInP/GaAs design[3] while considering (i) calibration and adjustment of the illumination light-source; (ii) confirmation of the consistency of results by incident photon-to-current efficiency (IPCE), and (iii) definition and confinement of the active area of the device. We initially measured 21.8% STH efficiency (black dashed line) using a tungsten white-light source, a calibrated GaInP photovoltaic reference cell, and epoxy-encased photocathodes. In contrast, integrating experimental IPCE over the AM 1.5G solar irradiance showed that less than 10% STH conversion appeared conceivable. We then performed a set of on-sun measurements that gave 16.1% STH (black line), before eliminating indirect light coupled to the sample by using a collimating tube and 13.8% STH efficiency (blue line) thereafter. However, the value still vastly exceeded the current density expected according to the quantum efficiency measured via IPCE. Finally, suspecting that the illuminated area is poorly defined by epoxy, we use a compression cell for an epoxy-free area definition, resulting in 9.3% STH efficiency (red line) – a number also compatible with our IPCE results. We propose applying the following standards for future PEC performance reporting: (i) traceable disclosure of the illumination-source configuration (lamp, filters, optics, PEC configuration) and/or its measured spectral distribution; (ii) thorough device-area definition (including confinement of the illumination area and avoidance of indirect light paths); (iii) complementary IPCE confirmation of the solar-generation potential; and (iv) proper consideration of faradaic efficiency. [1] H. Döscher, J. L. Young, J. F. Geisz, J. A. Turner, and T. G. Deutsch, “Solar to hydrogen efficiency: Shining light on phoelectrochemical device performance,” Energy Environ. Sci.2015. [2] H. Döscher, J. F. Geisz, T. G. Deutsch, and J. A. Turner, “Sunlight absorption in water – efficiency and design implications for photoelectrochemical devices,” Energy Environ. Sci.2014. [3] O. Khaselev and J. A. Turner, “A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting,” Science. 1998. Figure 1

ChemInform Abstract: Experimental Demonstrations of Spontaneous, Solar‐Driven Photoelectrochemical Water Splitting

AbstractReview: 109 refs.

Overall Photoelectrochemical Water Splitting using Tandem Cell under Simulated Sunlight.

A stand-alone photoelectrochemical (PEC) water-splitting system driven only by sunlight was demonstrated with a tandem-scheme of Pt/CdS/CuGa3 Se5 /(Ag,Cu)GaSe2 photocathode and NiOOH/FeOOH/Mo:BiVO4 photoanode in a neutral phosphate buffer solution as an electrolyte. The as-prepared semi-transparent Mo:BiVO4 layer allows sunlight to pass through the top photoanode and reach the bottom photocathode. Consequently, the tandem cell showed stoichiometric hydrogen and oxygen evolution with a solar-to-hydrogen (STH) conversion efficiency of 0.67 % over 2 h without degradation. The stability and STH efficiency are the highest among similar configuration of PEC tandem cells.

Efficiency analysis of a solar photovoltaic array coupled with an electrolyser power unit: a case study

ABSTRACTHydrogen as an energy carrier is one of the most potential candidates for clean energy and can be produced by water electrolysis. The use of 10 kW photovoltaic arrays for supplying a 5 kW electrolyser which consists of 10 series-connected electrolyser stacks and a 28% alkaline (KOH) solution electrolyte has been investigated at the Taleghan renewable energies site in Iran. The hydrogen produced by the electrolyser provides energy for the 1 kW polymer electrolyte membrane fuel cell, which meets the load when the solar energy is insufficient. Variations of the solar radiation intensity, the hydrogen production rate, the solar hydrogen efficiency and the overall efficiency of the solar hydrogen energy unit were monitored in detail. The overall energy efficiency was found to range from 0.93% to 5.01%. The obtained results demonstrate the great potential of such a power system for producing and storing energy in a solar-belt country like Iran.

A 24.4% solar to hydrogen energy conversion efficiency by combining concentrator photovoltaic modules and electrochemical cells

The highest efficiency of 24.4% for the solar-to-hydrogen (STH) energy conversion was obtained in an outdoor field test by combining concentrator photovoltaic (CPV) modules with InGaP/GaAs/Ge three-junction cells and polymer-electrolyte electrochemical (EC) cells. The high efficiency was obtained by using the high-efficiency CPV modules (∼31% under the present operation conditions) and the direct connection between the CPV modules and the EC cells with an almost optimized number of elements in series. The STH efficiency bottleneck was clarified to be the efficiency of the CPV modules, the over-potential of the EC cells, and matching of the operation point to the maximal-power point of the CPV modules.

Nitrogen and cobalt co-doped zinc oxide nanowires – Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting has been considered as a promising and environmentally benign approach for efficient and economic hydrogen generation by utilization of solar energy. Development of semiconductor materials with low band gap, high photoelectrochemical activity and stability has been of particular interest for a viable PEC water splitting system. In this study, Co doped ZnO, .i.e., (Zn0.95Co0.05)O nanowires (NWs) was selected as the composition for further co-doping with nitrogen by comparing solar to hydrogen efficiency (SHE) of ZnO NWs with that of various compositions of (Zn1−xCox)O NWs (x = 0, 0.05, 0.1). Furthermore, nanostructured vertically aligned Co and N-doped ZnO, .i.e., (Zn1−xCox)O:N NWs (x = 0.05) have been studied as photoanodes for PEC water splitting. An optimal SHE of 1.39% the highest reported so far to the best of our knowledge for ZnO based photoanodes was obtained for the co-doped NWs, (Zn0.95Co0.05)O:N - 600 NWs generated at 600 °C in ammonia atmosphere. Further, (Zn0.95Co0.05)O:N-600 NWs exhibited excellent photoelectrochemical stability under illumination compared to pure ZnO NWs. These promising results suggest the potential of (Zn0.95Co0.05)O:N-600 NWs as a viable photoanode in PEC water splitting cell. Additionally, theoretical first principles study conducted explains the beneficial effects of Co and N co-doping on both, the electronic structure and the band gap of ZnO.

Efficient Solar-to-Hydrogen Production Materials and Devices

Renewable hydrogen production via water splitting needs to tackle the challenges of high solar-to-hydrogen (STH) efficiency and high stability of the materials and devices. For photoelectrochemical (PEC) water splitting, semiconductor materials’ band gap, band edge, optoelectronic efficiency, and stability must be satisfied simultaneously to tackle the challenge. With over five decades of research, different materials and devices have been studied and explored. STH efficiencies of metal oxides have been limited by issues related to the wide band gap, absorption, charge mobility, recombination, interfacial kinetics, etc., those the material class may be stable. Thin films (like III-V and CIGS) offer alternative pathways to efficient STH conversion, with stability remains an issue. On the other hand, structures and configurations have been developed for unbiased PEC water splitting, mostly in laboratory scale. This presentation will address semiconductor materials, structures and devices developed for solar hydrogen production.

(Invited) Benchmarking a Metal Oxide-Based Thermochemical Cycle for Solar Hydrogen Production

It is estimated that growth in global population and continued industrialization of developing countries will double world energy consumption by 20351. This rising demand for energy will be largely met by burning fossil fuels, thereby increasing anthropogenic carbon in the atmosphere and fuelling the socioeconomic strife associated with climate change. Developing transformational energy technologies that efficiently and cost-effectively convert solar energy into simple chemical fuels is therefore necessary in order to realize a carbon-neutral, sustainable energy future. In this talk we will critically assess a two-step, high temperature thermochemical water splitting (WS) cycle powered by concentrated solar energy. This conceptually simple technology, outlined in Figure 1, can theoretically achieve greater solar-to-hydrogen (STH) conversion efficiency than alternative WS routes such as photosynthesis (natural or artificial) or photovoltaic-driven electrolysis2. However, many engineering and material science challenges must be overcome to demonstrate economic viability at large scales. Cost and scalability issues for solar thermal hydrogen production will be addressed within the context of a particle-based solar receiver reactor concept3–5developed at Sandia through a multi-year research initiative sponsored by the US Department of Energy. Key design principles will be reviewed and create a framework for discussing the synergistic interplay of materials chemistry, reactor design, and system operation necessary for this technology to achieve optimal STH conversion efficiency. The successful implementation of this solar energy conversion technology is predicated on meeting stringent requirements for cost and scalability that are deeply rooted in STH efficiency. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000. (1) International Energy Outlook 2011; DOE/EIA-0484(2011); U.S. Energy Information Administration, DOE/EIA-0484(2011) | September, 2011. (2) Siegel, N. P.; Miller, J. E.; Ermanoski, I.; Diver, R. B.; Stechel, E. B. Ind. Eng. Chem. Res. 2013, 52, 3276–3286. (3) Ermanoski, I.; Siegel, N. P.; Stechel, E. B. J. Sol. Energy Eng. 2013, 135, 031002. (4) Ermanoski, I.; Miller, J. E.; Allendorf, M. D. Phys. Chem. Chem. Phys. 2014, 16, 8418. (5) Ermanoski, I. Int. J. Hydrog. Energy 2014, 39, 13114–13117. Figure 1

Aluminum plasmonics for enhanced visible light absorption and high efficiency water splitting in core-multishell nanowire photoelectrodes with ultrathin hematite shells.

The poor internal quantum efficiency (IQE) arising from high recombination and insufficient absorption is one of the critical challenges toward achieving high efficiency water splitting in hematite (α-Fe2O3) photoelectrodes. By combining the nanowire (NW) geometry with the localized surface plasmon resonance (LSPR) in semiconductor-metal-metal oxide core-multishell (CMS) NWs, we theoretically demonstrate an effective route to strongly improve absorption within ultrathin (sub-50 nm) hematite layers. We show that Si-Al-Fe2O3 CMS NWs exhibit photocurrent densities comparable to Si-Ag-Fe2O3 CMS and outperform Fe2O3, Si-Fe2O3 CS and Si-Au-Fe2O3 CMS NWs. Specifically; Si-Al-Fe2O3 CMS NWs reach photocurrent densities of ∼ 11.81 mA/cm(2) within a 40 nm thick hematite shell which corresponding to a solar to hydrogen (STH) efficiency of 14.5%. This corresponds to about 93% of the theoretical maximum for bulk hematite. Therefore, we establish Al as an excellent alternative plasmonic material compared to precious metals in CMS structures. Further, the absorbed photon flux is close to the NW surface in the CMS NWs, which ensures the charges generated can reach the reaction site with minimal recombining. Although the NW geometry is anisotropic, the CMS NWs exhibit polarization independent absorption over a large range of incidence angles. Finally, we show that Si-Al-Fe2O3 CMS NWs demonstrate photocurrent densities greater than ∼ 8.2 mA/cm(2) (STH efficiency of 10%) for incidence angles as large as 45°. These theoretical results strongly establish the effectiveness of the Al-based CMS NWs for achieving scalable and cost-effective photoelectrodes with improved IQE, enabling a novel route toward high efficiency water splitting.

Modeling Practical Performance Limits of Photoelectrochemical Water Splitting Based on the Current State of Materials Research

Photoelectrochemical (PEC) water splitting is a means to store solar energy in the form of hydrogen. Knowledge of practical limits for this process can help researchers assess their technology and guide future directions. We develop a model to quantify loss mechanisms in PEC water splitting based on the current state of materials research and calculate maximum solar-to-hydrogen (STH) conversion efficiencies along with associated optimal absorber band gaps. Various absorber configurations are modeled considering the major loss mechanisms in PEC devices. Quantitative sensitivity analyses for each loss mechanism and each absorber configuration show a profound impact of both on the resulting STH efficiencies, which can reach upwards of 25 % for the highest performance materials in a dual stacked configuration. Higher efficiencies could be reached as improved materials are developed. The results of the modeling also identify and quantify approaches that can improve system performance when working with imperfect materials.

A Single Chip Standalone Water Splitting Photoelectrochemical Cell

Water splitting photoelectrochemical cell (PEC) was fabricated in which the electrolyzer parts were made on a single chip. This was achieved by depositing an optically transparent Mn-oxide-TiO2 thin layer on the front of a triple junction amorphous Si photovoltaic cell which acted as the anode and the back stainless steel layer acted as the cathode under illumination of light. This single chip water electrolysis cell operates like an artificial leaf. Water splitting was observed by simply submersing the device in a basic electrolyte solution under solar simulated light of 1 sun (0.1 W cm-2). This self-driven PEC was found to produce hydrogen gas at the rate of 12.42 L m-2 h-1 and a solar to hydrogen efficiency (STHE) of 3.25 % from the collected H2 gas in 2.5 M KOH solution. No signs of degradation of this single chip PEC were observed during water splitting when the device was run continuously for 6 hours.

Photoexcitation of TiO2 photoanode in water splitting

TiO2 is one of the most promising photoanodes for solar-hydrogen conversion by water splitting. However, the solar-hydrogen efficiency of TiO2 remains limited because of a low photocurrent generation. A clear understanding of photoexcitations within photoanodes can predict the quantity of photocurrent and consequently determine the solar-hydrogen efficiency. In this work, hydrothermally synthesized rutile TiO2 nanorods were investigated for their photoelectrochemical (PEC) performance. A photogenerated hole concentration of TiO2 photoanode was derived as 8.40 × 1014 cm−3 under one sun illumination. In addition, Fermi level pinning associated with high density of surface states was also observed under PEC operation. Base on these results, a series of band diagrams of TiO2 photoanode were established to describe the photogeneration of holes and current at various bias potential. The main limitation of photocurrent generation is the distribution of surface-trapped states, which determines the hole concentration at the surface and consequently determines the open-circuit potential and the photocurrent density.

The energy efficiency of carbon dioxide fixation by a hydrogen-oxidizing bacterium

Fixing carbon dioxide (CO2) with solar hydrogen (H2) is a novel alternative to conventional photosynthesis of plants and microalgae. The energy efficiency of CO2 fixation by a hydrogen-oxidizing bacterium was investigated in a closed reactor system. The molar ratio of consumed H2 and CO2 was measured under mass transfer limitation in atmospheres of sufficient H2, low CO2, and a broad range of O2. The energy efficiency, ranging from 10% to 60%, was primarily affected by the oxygen concentration (6–30 mol%). The research revealed a clear trend that a low oxygen concentration gave high energy efficiency, but slow gas consumption. A high energy efficiency of 50% was measured under a moderate oxygen concentration (10 mol%). Based on 10% solar hydrogen efficiency, a 5% overall efficiency from solar energy to biomass can therefore be achieved.

Net primary energy balance of a solar-driven photoelectrochemical water-splitting device

A fundamental requirement for a renewable energy generation technology is that it should produce more energy during its lifetime than is required to manufacture it. In this study we evaluate the primary energy requirements of a prospective renewable energy technology, solar-driven photoelectrochemical (PEC) production of hydrogen from water. Using a life cycle assessment (LCA) methodology, we evaluate the primary energy requirements for upstream raw material preparation and fabrication under a range of assumptions of processes and materials. As the technology is at a very early stage of research and development, the analysis has considerable uncertainties. We consider and analyze three cases that we believe span a relevant range of primary energy requirements: 1550 MJ m−2 (lower case), 2110 MJ m−2 (medium case), and 3440 MJ m−2 (higher case). We then use the medium case primary energy requirement to estimate the net primary energy balance (energy produced minus energy requirement) of the PEC device, which depends on device performance, e.g. longevity and solar-to-hydrogen (STH) efficiency. We consider STH efficiency ranging from 3% to 10% and longevity ranging from 5 to 30 years to assist in setting targets for research, development and future commercialization. For example, if STH efficiency is 3%, the longevity must be at least 8 years to yield a positive net energy. A sensitivity analysis shows that the net energy varies significantly with different assumptions of STH efficiency, longevity and thermo-efficiency of fabrication. Material choices for photoelectrodes or catalysts do not have a large influence on primary energy requirements, though less abundant materials like platinum may be unsuitable for large scale-up.

An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

The solar-to-hydrogen (STH) efficiency limits, along with the maximum efficiency values and the corresponding optimal band gap combinations, have been evaluated for various combinations of light absorbers arranged in a tandem configuration in realistic, operational water-splitting prototypes. To perform the evaluation, a current–voltage model was employed, with the light absorbers, electrocatalysts, solution electrolyte, and membranes coupled in series, and with the directions of optical absorption, carrier transport, electron transfer and ionic transport in parallel. The current density vs. voltage characteristics of the light absorbers were determined by detailed-balance calculations that accounted for the Shockley–Queisser limit on the photovoltage of each absorber. The maximum STH efficiency for an integrated photoelectrochemical system was found to be ∼31.1% at 1 Sun (=1 kW m−2, air mass 1.5), fundamentally limited by a matching photocurrent density of 25.3 mA cm−2 produced by the light absorbers. Choices of electrocatalysts, as well as the fill factors of the light absorbers and the Ohmic resistance of the solution electrolyte also play key roles in determining the maximum STH efficiency and the corresponding optimal tandem band gap combination. Pairing 1.6–1.8 eV band gap semiconductors with Si in a tandem structure produces promising light absorbers for water splitting, with theoretical STH efficiency limits of >25%.

Effect of bulk doping and surface-trapped states on water splitting with hematite photoanodes

Hematite (α-Fe2O3) is an intensively studied photoanode for water splitting. However, the solar-hydrogen efficiency of an α-Fe2O3 photoanode remains limited because of its low conductivity and high surface recombination rate that limit its photocurrent output. In this work, hematite (α-Fe2O3) photoanodes prepared by electroplating were investigated for their majority and minority carrier concentration and surface-trapped states. The results show that the photocurrent generation strongly depends both on the bulk doping and the interface density of states (Dit). A high electron concentration (over 1.2 × 1020 cm−3) with high Dit (1.4 × 1016 cm−2 eV−1) may jeopardize the water splitting, with negligible photocurrent output under AM1.5 illumination. In contrast, a photocurrent is detected when the electron concentration and Dit is lower than 6.1 × 1019 cm−3 and 8.8 × 1014 cm−2 eV−1. This result has also been interpreted with the variation of the α-Fe2O3–electrolyte band diagram with the bias potential.

Hydrogen-Treated TiO2 Nanowire Arrays for Photoelectrochemical Water Splitting

We report the first demonstration of hydrogen treatment as a simple and effective strategy to fundamentally improve the performance of TiO(2) nanowires for photoelectrochemical (PEC) water splitting. Hydrogen-treated rutile TiO(2) (H:TiO(2)) nanowires were prepared by annealing the pristine TiO(2) nanowires in hydrogen atmosphere at various temperatures in a range of 200-550 °C. In comparison to pristine TiO(2) nanowires, H:TiO(2) samples show substantially enhanced photocurrent in the entire potential window. More importantly, H:TiO(2) samples have exceptionally low photocurrent saturation potentials of -0.6 V vs Ag/AgCl (0.4 V vs RHE), indicating very efficient charge separation and transportation. The optimized H:TiO(2) nanowire sample yields a photocurrent density of ∼1.97 mA/cm(2) at -0.6 V vs Ag/AgCl, in 1 M NaOH solution under the illumination of simulated solar light (100 mW/cm(2) from 150 W xenon lamp coupled with an AM 1.5G filter). This photocurrent density corresponds to a solar-to-hydrogen (STH) efficiency of ∼1.63%. After eliminating the discrepancy between the irradiance of the xenon lamp and solar light, by integrating the incident-photon-to-current-conversion efficiency (IPCE) spectrum of the H:TiO(2) nanowire sample with a standard AM 1.5G solar spectrum, the STH efficiency is calculated to be ∼1.1%, which is the best value for a TiO(2) photoanode. IPCE analyses confirm the photocurrent enhancement is mainly due to the improved photoactivity of TiO(2) in the UV region. Hydrogen treatment increases the donor density of TiO(2) nanowires by 3 orders of magnitudes, via creating a high density of oxygen vacancies that serve as electron donors. Similar enhancements in photocurrent were also observed in anatase H:TiO(2) nanotubes. The capability of making highly photoactive H:TiO(2) nanowires and nanotubes opens up new opportunities in various areas, including PEC water splitting, dye-sensitized solar cells, and photocatalysis.