An Integrated Device View on Photo-Electrochemical Solar-Hydrogen Generation

Modestino, Miguel A.; Haussener, Sophia

doi:10.1146/annurev-chembioeng-061114-123357

Cited by 67 publications

(61 citation statements)

References 117 publications

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“…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.…”

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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“…9 Performing water electrolysis from the vapor phase exhibits several advantages: lower water splitting potential, lack of bubble evolution at the catalyst surface, and simplified implementation of the electrolyzer by direct humid air-based operation. 9,10 On the downside, water splitting under humid air poses significant transport challenges, as the low concentration of water can limit the water-splitting rates in the device. The operation of vapor-fed electrolyzers requires all of the ionic current between the reaction sites to be transported by a solid state ion conductor (i.e.…”

Section: Introductionmentioning

confidence: 99%

Vapor-fed microfluidic hydrogen generator

et al. 2015

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Water-splitting devices that operate with humid air feeds are an attractive alternative for hydrogen production as the required water input can be obtained directly from ambient air. This article presents a novel proof-of-concept microfluidic platform that makes use of polymeric ion conductor (Nafion®) thin films to absorb water from air and performs the electrochemical water-splitting process. Modelling and experimental tools are used to demonstrate that these microstructured devices can achieve the delicate balance between water, gas, and ionic transport processes required for vapor-fed devices to operate continuously and at steady state, at current densities above 3 mA cm. The results presented here show that factors such as the thickness of the Nafion films covering the electrodes, convection of air streams, and water content of the ionomer can significantly affect the device performance. The insights presented in this work provide important guidelines for the material requirements and device designs that can be used to create practical electrochemical hydrogen generators that work directly under ambient air. Broader contextThe large scale deployment of hydrogen production technologies can be triggered by the development of electrolytic devices that function continuously under simple operation schemes. Water-splitting devices that operate under humid air are an attractive alternative to classic alkaline or proton exchange membrane electrolysis systems. In this regard, the implementation of water splitting technologies can be significantly simplified as the water feed could be obtained directly from the environment. Using polymeric ion-conducting materials in a microfluidic platform, this work balances the transport processes that are inherently limiting in devices operated with diluted water feeds, and demonstrates for the first time a vapor-fed microelectrolyzer capable of generating hydrogen at initial current densities above 10 mA cm −2

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“…Most of these devices show short lifetimes (<1 day), low efficiencies, or use materials and designs that would prevent their practical and economical implementation. 6,8 Deployable solar-hydrogen devices would need to function stably for years, produce robustly and continuously nearly pure H 2 streams, incorporate economically viable photovoltaic and water-splitting components, and operate at high efficiencies so that the energy produced over their lifetime is much greater than the energy required to fabricate and operate the devices. 9,10 Currently, the best performing systems implement GaAs-based photovoltaic materials to reach high conversion efficiencies.…”

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Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts

Schüttauf

Modestino

Chinello

et al. 2016

J. Electrochem. Soc.

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Affordable, stable and earth-abundant photo-electrochemical materials are indispensable for the large-scale implementation of sunlight-driven hydrogen production. Here we present an intrinsically stable and scalable solar water splitting device that is fully based on earth-abundant materials, with a solar-to-hydrogen conversion efficiency of 14.2%. This unprecedented efficiency is achieved by integrating a module of three interconnected silicon heterojunction solar cells that operates at an appropriate voltage to directly power microstructured Ni electrocatalysts. Nearly identical performance levels were also achieved using a customized state-of-the-art proton exchange membrane (PEM) electrolyzer. The past decade has seen an increase in the urgency to substitute fossil fuels with clean and renewable energy sources. Among all of the renewable sources, solar irradiation is undeniably the most prominent option. The average accessible solar power accounts for over ∼120 000 TW globally; 1 several thousand times the current global energy needs.2 Photovoltaic cells can capture this vast energy resource and convert it into usable electrical energy at high efficiencies. Their implementation in the past years has seen a large growth driven by favorable environmental policies and a steady decrease in their production cost. Although the penetration of photovoltaics has been significant, some challenges for their integration into the electricity grid have started to become evident. Mainly, the intermittent nature of the solar electricity production prevents their large-scale grid implementation without compensation mechanisms that satisfy the demand during low-irradiation periods. Adding energy storage capacity to the grid could directly alleviate the fluctuations on power production. Electrochemical energy storage in batteries is already an interesting option for large-scale stationary energy storage. Electrochemical production of hydrogen from excess solar electricity is also an attractive option for storing solar energy in the form of a fuel which could be used at a later stage for electricity production back into the grid or transportation. 3,4 Furthermore, hydrogen can be stored for prolonged periods of time, so that solar resources are harvested during high irradiation periods and used throughout the year. Because of these multiple advantages, solar-to-fuel approaches have attracted a lot of interest in the renewable energy field and project themselves as a critical technology to achieve large-scale utilization of solar-energy sources. 5-7Despite the strong research interest on solar-hydrogen materials and technologies, there have only been a limited number of demonstrations of solar water splitting devices. Most of these devices show short lifetimes (<1 day), low efficiencies, or use materials and designs that would prevent their practical and economical implementation. 6,8 Deployable solar-hydrogen devices would need to function stably for years, produce robustly and continuously nearly pure H 2 streams, incorporate ...

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An Integrated Device View on Photo-Electrochemical Solar-Hydrogen Generation

Cited by 67 publications

References 117 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

Vapor-fed microfluidic hydrogen generator

Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts

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