These tables list the U.S. Department of Energy (DOE) technical targets and example cost and performance parameter values that achieve the targets for hydrogen production from photoelectrochemical water splitting. The tables are organized into separate sections for photoelectrode systems and dual bed photocatalyst systems.

More information about targets can be found in the Hydrogen Production section of the Fuel Cell Technologies Office's Multi-Year Research, Development, and Demonstration Plan.

Photoelectrode Systems

Technical Targets: Photoelectrochemical Hydrogen Production: Photoelectrode System with Solar Concentration ^a

^a The targets in this table are for research tracking with the Ultimate Target values corresponding to market competitiveness. Targets are based on an initial analysis utilizing the H2A Central Production Model 3.0 with the standard H2A economic parameters. Targets are based on photoelectrode-type PEC systems wherein a solar trough collector concentrates light onto a PEC receiver assembly. The PEC receiver consists of a flat panel PEC electrode (submerged in an electrolyte bath) and the collection housing and manifolds to collect and separate the evolved hydrogen and oxygen gases. Solar concentration is assumed to be 15:1 for the ultimate target case and 10:1 for all others. Further analysis assumptions may be found in "Technoeconomic Analysis of Photoelectrochemical (PEC) Hydrogen Production," Directed Technologies Inc., Final Report to the Department of Energy, December 2009. Plant assumed capacity is 50,000 kg H₂/day for all years. All targets are expressed in 2007 dollars.
^b Hydrogen cost represents the complete system hydrogen production cost for purified, 300 psi compressed gas. System level losses and expenses due to solar collection/concentration, window transmittance/refraction, replacement parts, operation, and maintenance are included in the cost calculations which are documented in the H2A v3 Future Case study for Type 4 (Photoelectrode System with Concentration) Photoelectrochemical (PEC) Production of Hydrogen.
^c Capital cost includes solar concentration and associated tracking (if any), the optical window, and the water/electrolyte/gas containment subsystem. The cost of the PEC electrode is not included. All areas refer to total solar capture area. While improvements beyond the current status are needed to meet these cost goals, this area is not presently a research focus of the Fuel Cell Technologies Office.
^d Annual electrode cost refers to the annual replacement cost of the PEC photoelectrode panel normalized by the design capacity of the system (in metric tons H₂ per day). Electrode cost includes both the material and manufacturing cost of the PEC electrode used within the reactor.
^e STH energy conversion ratio is defined as the energy of the net hydrogen produced (LHV) divided by full-spectrum solar energy consumed. For systems utilizing solar energy input only, the consumed energy is calculated based on the incident irradiance over the total area of the solar collector. For hybrid systems, all additional non-solar energy sources (e.g., electricity) must be included as equivalent solar energy inputs added to the denominator of the ratio.
^f The 2011 Status of STH ratio is in the range of 4% and 12% for different semiconductor material systems exhibiting different levels of operational durability. Thin film material systems have been demonstrated with STH >4% for hundreds of hours (A. Madan, Fuel Cell Technologies Program 2011 Annual Progress Report; Crystalline material systems have been demonstrated with STH >12% for tens of hours. [O. Khaselev, J.A. Turner, Science 280, 425 (1998)].
^g The hydrogen production rate in kg/s per total area of solar collection under full-spectrum 1-sun incident irradiance (1,000 W/m²). Under ideal conditions, STH can be related to this rate as follows: STH = H₂ Production Rate (kg/s per m²) * 1.23E8 (J/kg) / 1.00E3 (W/m²). Measurements of the 1-sun hydrogen production rate can provide an invaluable diagnostic tool in the evaluation of loss mechanisms contributing to the STH ratio.

Example Parameter Values to Meet Cost Targets: Photoelectrochemical Hydrogen Production (Photoelectrode System)

^a PEC photoelectrode cost refers to the material and manufacturing cost of the PEC electrode. Area is based on the actual area of the electrode itself.
^b This parameter is the PEC photoelectrode cost (as defined above) normalized by the metric tons per day of hydrogen design capacity of the electrode.
^c Electrode replacement lifetime denotes the projected total duration of the electrode being immersed in electrolyte and under cyclic solar illumination until process energy efficiency drops to 80% of its original values. Thus, a 10-year electrode replacement lifetime refers to 10 years of operation under diurnal cycles and approximately 5 years of actual hydrogen production.
^d This parameter denotes non-electrode, non-concentrator/PEC receiver, non-installation balance of plant costs normalized by the metric tons per day of hydrogen design capacity of the electrode.

Dual Bed Photocatalyst Systems

Technical Targets: Photoelectrochemical Hydrogen Production: Dual Bed Photocatalyst System ^a

^a The targets in this table are for research tracking with the Ultimate Target values corresponding to market competitiveness. Targets are based on an initial analysis utilizing the H2A Central Production Model 3.0 with standard H2A economic parameters. Targets are based on a dual-bed PEC nanoparticle slurry-type system wherein clear thin film polymer bag-style reactors are filled with water and photocatalytically active nanoparticles. The hydrogen evolution half-reaction occurs in one bag reactor section and the oxygen evolution half-reaction occurs in an adjacent reactor section. The reactor sections are connected by a porous ionic bridge which permits ion exchange to complete the electrochemical circuit but prevents gas mixing. Solar energy energizes both reactions. No solar concentration is used. Further analysis assumptions may be found in "Technoeconomic Analysis of Photoelectrochemical (PEC) Hydrogen Production," Directed Technologies Inc., Final Report to the Department of Energy, December 2009. Plant capacity is 50,000 kg H₂/day for all years. All targets are expressed in 2007 dollars.
^b Hydrogen cost represents the complete system hydrogen production cost for purified, 300 psi compressed gas. System level losses and expenses due to solar window transmittance/refraction, replacement parts, operation, and maintenance are included in the cost calculations which are documented in the H2A v3 Future Case study for Type 2 (PEC Dual Bed Photocatalyst System) Photoelectrochemical Production of Hydrogen.
^c PEC particle cost refers to the annual replacement cost of the PEC nanoparticles normalized by the design capacity of the system (metric tons H₂ per day). Particle cost includes both the material and manufacturing cost of the PEC nanoparticles used within the reactor. Although different chemical reactions occur in the two bed sections, particle cost is combined for purposes of cost reporting.
^d STH energy conversion ratio is defined as the energy of the net hydrogen produced (LHV) divided by full-spectrum solar energy consumed. For systems utilizing solar energy input only, the consumed energy is calculated based on the incident irradiance over the total area of the solar collector. For hybrid systems, all additional non-solar energy sources (e.g., electricity) must be included as equivalent solar energy inputs added to the denominator of the ratio. In a dual bed system, this requires two material systems each with half reactions operating at twice the stated net STH energy conversion ratio.
^e Dual bed systems are less mature than photoelectrode PEC systems. The current status STH energy conversion ratio is still under investigation.
^f The hydrogen production rate in kg/s per total area of solar collection under full-spectrum 1-sun incident irradiance (1,000 W/m²). Under ideal conditions, STH can be related to this rate as follows: STH = H₂ Production Rate (kg/s per m²) * 1.23E8 (J/kg) / 1.00E3 (W/m²). Measurements of the 1-sun hydrogen production rate can provide an invaluable diagnostic tool in the evaluation of loss mechanisms contributing to the STH ratio.

Example Parameter Values to Meet Cost Targets: Photoelectrochemical Hydrogen Production (Dual Bed Photocatalyst)

^a PEC particle cost refers to the material and manufacturing cost of the PEC nanoparticles used within the reactor. While different chemical reactions occur in the two bed sections, the particle costs are combined for purposes of cost reporting. Particle mass is based on the total particle mass (including inert substrate if used).
^b Particle replacement lifetime denotes the projected total duration of the nanoparticles being immersed in electrolyte and under cyclic solar illumination until process energy efficiency drops to 80% of its original values. Thus, a 5-year particle replacement lifetime refers to 5 years of operation under diurnal cycles and approximately 2.5 years of actual hydrogen production.
^c Reactor system capital cost includes only the high density polyethylene clear plastic film reactor bed assembly and its associated ionic transfer bridges. Installation, fluid piping, and the photocatalytic nanoparticles are not included. All areas refer to total solar capture area.
^d This parameter denotes the non-installed balance of plant costs exclusive of reactor beds and PEC particles. It includes piping, controls, sensors, pumps, and compressors and is normalized by the metric tons per day of hydrogen design capacity of the system.