3D printed flow plates for the electrolysis of water: an economic and adaptable approach to device manufacture

415

347

Although polymer electrolyte water electrolyzers (PEWEs) have been used in small-scale (kW to tens of kW range) applications for several decades, PEWE technology for hydrogen production in energy applications (power-to-gas, power-to-fuel, etc.) requires significant improvements in the technology to address the challenges associated with cost, performance and durability. Systems with power of hundreds of kW or even MWs, corresponding to hydrogen production rates of around 10 to 20 kg/h, have started to appear in the past 5 years. The thin (∼0.2 mm) polymer electrolyte in the PEWE with low ohmic resistance, compared to the alkaline cell with liquid electrolyte, allows operation at high current densities of 1-3 A/cm 2 and high differential pressure. This article, after an introductory overview of the operating principles of PEWE and state-of-the-art, discusses the state of understanding of key phenomena determining and limiting performance, durability, and commercial readiness, identifies important 'gaps' in understanding and essential development needs to bring PEWE science & engineering forward to prosper in the energy market as one of its future backbone technologies. For this to be successful, science, engineering, and process development as well as business and market development need to go hand in hand. In 2015, the global primary energy consumption was 153 PWh, 1 corresponding to an average rate of energy conversion of 17 TW. About 30% (∼6 TW) of this is used for electricity generation, which yields around 2.8 TW of electrical power (24 PWh per year). Around two thirds of the electricity is generated from fossil fuels, hydropower contributes 16%, nuclear power 11%, and other renewables (such as solar and wind) only 6.7%.1 Solar (photovoltaics) and wind power have a combined installed capacity of about 660 GW (in 2015).2 Electricity supply based on a significant share of these "new renewables" is associated with large discrepancies between supply and demand, owing to the intermittent nature of these primary energy sources. Hence, solutions for the grid-scale storage of electricity need to be developed and implemented. The electrochemical splitting of water (electrolysis) is a clean and efficient process offering interesting prospects to store large amounts of excess electricity in form of chemical energy ('power-to-gas' concept). 3,4 The produced hydrogen and oxygen can be used to regenerate electricity in periods of low production and high demand or serve as clean transportation fuel for fuel cell electric vehicles. Therefore, water electrolysis is a key technology in future sustainable energy scenarios, since hydrogen as an energy 'vector', i.e., as a universal energy carrier, could promote the decarbonization of the energy economy, or even become its backbone in the context of a 'hydrogen economy'.5 Moreover, the produced hydrogen can be used to methanate CO 2 from suitable sources, such as biogas plants, to produce synthetic natural gas (SNG), which can be injected and stored in the natural gas network. 6...

Section: Materials and Componentsmentioning

confidence: 99%

Critical Review—Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development

Babic

Suermann

Büchi

et al. 2017

415

347

“…Relatively low fuel cell performance is observed as a result of the low operating temperature and the high resistive losses of the current collection method. Other 3D printing techniques such as selective laser sintering or metallic deposition 27,28 could be used to create a conductive 3D printed flow field; however, this would result in substantial loss in visualization capabilities using XCT. Subsequently following diagnostic measurement, the cell was equilibrated for 2 hrs at 0.1 A cm −2 , followed by disconnection of load, closure of all inlet and outlet ports and installation of the cell assembly in the XCT system for imaging.…”

Section: Methodsmentioning

confidence: 99%

3D Printed Flow Field and Fixture for Visualization of Water Distribution in Fuel Cells by X-ray Computed Tomography

White

Orfino

Hannach

et al. 2016

This work demonstrates an original approach to three-dimensional, high-resolution, non-destructive visualization of fuel cells during room temperature operation using a commercial micro-X-ray computed tomography (XCT) system. The novel application of 3D printing technology was used to create a customized housing fixture that allows for non-invasive imaging of an operational fuel cell. The use of 3D print materials also allows for rapid prototyping and intricate design of any experimental fixture with minimal cost. Demonstration of imaging capabilities is shown through in situ visualization of the internal MEA components and liquid water after fuel cell operation. Water imaging in fuel cells is particularly challenging using XCT due to small differences in X-ray absorption characteristics between constituent materials. Image processing operations are discussed which allows for the improved segmentation of solid and water to calculate porosity and saturation throughout the gas diffusion layer, as reported herein. Additionally, a membrane thickness increase of approximately 25% due to swelling under 100% relative humidity is shown, which has previously been difficult to determine. Overall, the results shown here illustrate the novel use of 3D printed materials and image processing steps to be further used in understanding of fuel cell devices through non-invasive imaging procedures by use in a commercial micro-XCT system. Polymer electrolyte fuel cells (PEFC) have significant potential for automotive applications as an alternate clean energy technology with zero emissions at the point of use. The many advantages include quick start-up time, low operating temperature, low weight, high efficiency and relatively simple design as compared to other clean energy solutions.1 Despite these advantages, however, a primary reason for the delay of this technology from meeting commercial automotive application standards is cost. Significant cost reductions are possible by increasing the power density, which is currently limited by liquid water related mass transport effects at high current densities.2 Higher power density cells also have an advantage for automotive applications due to a better form factor for vehicles. In other fuel cell technologies such as back-up power in extreme climates or mobile fuel cell applications, fuel cells operating at low temperature or low gas flow rates are susceptible to flooding. Flooding, or channel clogging, may lead to significantly reduced performance from inaccessibility of reactant gas flow as well as non-uniform reactant distribution in fuel cell stacks. 3,4 Proper understanding of water management in operating fuel cells is imperative to the design and implementation of higher power density fuel cells and is thus a highly researched field of PEFC performance.Current fuel cell diagnostic methods typically involve investigation by empirical testing and ex situ analysis. A common technique for fuel cell investigatory research is to use scanning electron microscopy (SEM), which provides hi...

“…The flow plates were covered with a thin layer of silver conductive paste from Sigma-Aldrich, and a 500 nm gold film was evaporated using an EVA760 alliance concept electron beam evaporator. 29 The MEA was sealed inside a pair of flow plates with a set of titanium (Ti) gas diffusion layers (GDLs) as shown in Figure S3 in the Supplementary Information. Two different GDLs were implemented to assure uniform electrical resistance and facile water and gas transport.…”

Section: Methodsmentioning

confidence: 99%

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

Schüttauf

Modestino

Chinello

et al. 2016

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 ...