A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO<sub>2</sub> films

Verlage, Erik; Hu, Shu; Li, Rui; Jones, Ryan J. R.; Sun, Ke; Xiang, Chengxiang; Lewis, Nathan S.; Atwater, Harry A.

doi:10.1039/c5ee01786f

Cited by 274 publications

(263 citation statements)

References 57 publications

(149 reference statements)

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“…19,21 Ohmic losses are often minimized by using concentrated acid or alkaline electrolytes such as H 2 SO 4 , HClO 4 , or KOH at concentrations of 0.5 M or higher. 4,5,14,22,23 In wireless systems with flat monoliths consisting of dense PV and electrocatalysts mounted on either side, ions need to travel around the dense monolith to cover the distance between anode and cathode. Already at the centimeter scale unacceptable ohmic losses of hundreds of millivolts and more are to be expected.…”

Section: ■ Introductionmentioning

confidence: 99%

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

et al. 2016

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Monolithic solar water splitting devices consist of photovoltaic materials integrated with electrocatalysts and produce solar hydrogen by water splitting upon solar illumination in one device. Upscaling of monolithic solar water splitting devices is obstructed by high ohmic losses in the electrolyte due to long ionic transport distances. A new design overcomes the problem by introducing micron sized pores in a silicon wafer substrate coated with electrocatalysts. A porous solar hydrogen device was simulated by applying a current corresponding to ca. 10% solar-to-hydrogen efficiency. Porous monoliths of 550 μm thickness with varying pore size and spacing were fabricated by laser ablation and electrochemically characterized. Ohmic losses well below 100 mV were reached at 14.4% porosity with 77 μm pores spaced 250 μm apart in 0.25 M KOH electrolyte. In 1 M KOH, 100 mV was reached at 6% porosity with 1 mm pore spacing. Our results suggest ohmic losses below 50 mV can be achieved when using 10 μm thick substrates at 0.2% porosity. These findings make it possible for monolithic solar water splitting devices to be scaled without loss of efficiency. ■ INTRODUCTIONHydrogen is one of the promising energy vectors that will likely be part of the future sustainable energy portfolio. 1 Using sunlight to split water into hydrogen and oxygen is a viable option for solar hydrogen production and several technologies exist that achieve water splitting at high efficiency. 2 A direct way to produce solar hydrogen is by using a solar water splitting device which combines light absorption, charge separation and electrochemical reactions in an integrated device. 3 High solarto-hydrogen (STH) efficiencies are reached using high-end photovoltaics (PV) coupled to electrocatalysts submerged in concentrated aqueous electrolyte. 4−7 The use of robust earthabundant catalysts and stable light absorbing materials with suitable band gaps has also been demonstrated. 8−11 These approaches show great promise at lab scale and development of practical systems is ongoing. 12−16 Beside the performance of catalysts and light absorbers, cell design is important and ohmic losses need to be minimized to maximize overall efficiency. 17,18 There are two common design types. 19,20 In the "wired" design ( Figure 1A) planar anode and cathode have opposed surfaces at close proximity such that the interelectrode distance to be covered by ions in the liquid electrolyte is minimized. 9−11 The "wireless" or "monolithic" layout ( Figure 1B) simplifies cell design by eliminating electrical contacts and wires through integration of all components in a monolithic flat assembly. 10

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Section: ■ Introductionmentioning

confidence: 99%

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

et al. 2016

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“…The key to this was a thin protective layer of titanium dioxide a few nanometers thick. In August, the group published the results of their reactor design, which can produce hydrogen fuel with 10% efficiency (5).…”

Section: Hydrogen Hopesmentioning

confidence: 99%

Liquid sunlight

Bourzac¹

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Although the active areas are typically small, <0.5 cm 2 , impressive efficiencies (up to 14%) and lifetimes of up to several days have been reached. 3,27 These devices are still in an early stage of development and so, it is yet unknown whether they can provide Figure 2. Left: Schematic drawing of the system showing the concept for solar collection and conversion to electricity and stored heat.…”

Section: Research Needs For Photoelectrochemical Fuel Productionmentioning

confidence: 99%

Perspectives on the photoelectrochemical storage of solar energy

Krol

Parkinson

2017

MRS Energy & Sustainability

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Direct photoelectrochemical water splitting offers several advantages over PV-powered electrolysis and may become the technology of choice in the future. However, significant R&D efforts and breakthroughs are needed to accomplish this goal.The sustainable production of hydrogen would be an important first step for both powering fuel cells and for enabling large-scale and technologically mature gas phase processes to reduce CO 2 and nitrogen to get desired products. Specifically, the central challenge is to produce hydrogen from water using sunlight. Photovoltaics and wind-powered electrolysis are likely to be the technology of choice to produce renewable hydrogen for the next few decades. However, the integration of light absorption and catalysis in 'direct' photoelectrolysis routes offers several advantages, such as lower current densities and better heat management, and may become technologically relevant in the second half of this century. This article discusses the research and development efforts and needed breakthroughs to achieve this goal. New chemically stable semiconductors with a band gap between 1.5 and 2.0 eV and long carrier lifetimes are urgently needed to make efficient tandem devices.Scale-up of these research level devices beyond a few cm 2 introduces mass transport limitations that require creative electrochemical engineering solutions. Last but not least, standardized methods for measuring efficiencies and stabilities need to be implemented and should lead to official benchmarking and certification laboratories to guide commercial scale up efforts. Keywords: photochemical; energy storage; energy generation RevIew DISCUSSION POINTS• Water splitting will be a central challenge for any future fossil fuel-free energy infrastructure that relies on liquid or gaseous chemical fuels.• While the main materials challenge for solar-and wind-driven electrolysis is the development of better catalysts, the main challenge for photoelectrochemical water splitting is to find new chemically stable optimal-bandgap semiconducting light absorbers.• Further progress in the development of photo-driven water splitting generators requires significant additional efforts in electrochemical engineering and the development of standardized methods for benchmarking device performance and stability.

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A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO₂ films

Abstract: A monolithically integrated device, protected by a TiO2 stabilization layer, splits water using sunlight.

Cited by 274 publications

References 57 publications

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

Liquid sunlight

Perspectives on the photoelectrochemical storage of solar energy

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A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO2 films

Abstract: A monolithically integrated device, protected by a TiO2 stabilization layer, splits water using sunlight.

Cited by 274 publications

References 57 publications

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

Minimization of Ionic Transport Resistance in Porous Monoliths for Application in Integrated Solar Water Splitting Devices

Liquid sunlight

Perspectives on the photoelectrochemical storage of solar energy

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A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO₂ films