Current density mapping and optical flow visualisation of a polymer electrolyte membrane water electrolyser

397

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: Transport Processes (2-phase)mentioning

confidence: 99%

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

Babic

Suermann

Büchi

et al. 2017

397

347

“…Besides electrochemical characterization, optical imaging using transparent cell designs was conducted to investigate flow regimes and mass transport. Dedigema et al 16,17 showed that the transition of two-phase flow in the flow channel from bubbly to slug flow improves fluidic transport. Arbabi et al 18,19 characterized oxygen bubble growth based on microfluidic chips mimicking the bulk properties of a PTL.…”

mentioning

confidence: 99%

Polymer Electrolyte Water Electrolysis: Correlating Porous Transport Layer Structural Properties and Performance: Part I. Tomographic Analysis of Morphology and Topology

Schuler

Bruycker

Schmidt

et al. 2019

114

171

In the first paper of this series, the bulk, surface and transport properties of porous transport layer materials (PTL) for polymer electrolyte water electrolysis cells (PEWE) are characterized. A systematic PTL matrix of Ti fiber materials with 3 fiber diameters and 2 nominal porosities as well as a state of the art sintered powder material are investigated to get a better understanding of the governing parameters in electrolysis cells. X-ray tomographic microscopy analysis of ex situ PTL structures and post operando membrane electrode assemblies is performed. On the tomographic structures, bulk (porosity, pore/solid size distributions, fiber orientation), mass transport (diffusivity, permeability, conductivities) and surface parameters (roughness, membrane deformation, PTL surface area and interfacial contact area) are determined. The second paper of this series will correlate the structural parameters with in-depth electrochemical analysis. The new insights into the effect of PTL properties on PEWE performance allow to isolate governing key parameters. From know-how obtained on the fiber based materials fundamental design guidelines for optimization of PTL structures are deduced.

“…Experimental analyses with a 250 cm 2 circular and a 50 cm 2 square cell have shown that the contact pressure and the resulting interfacial contact resistances may result in heavily nonhomogeneous CDDs, which can lead to local temperature hot-spots and consequently enhance local degradation processes. Other works from Sun et al, 8 Dedigama et al 9 and one own recent work 10 focused on the operating conditions and their effects on temperature distribution and in particular on the CDD along the channel coordinate.…”

mentioning

confidence: 99%

Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell

Immerz

Bensmann

Trinke

et al. 2018

The present analysis shows the local distribution of current density and EIS measurements along a 50 cm single-channel proton exchange membrane water electrolysis (PEMWE) cell. Measurements for operating modes with one sufficiently high and one insufficiently low stoichiometric water ratio (λ) were carried out to observe effects on the current density distribution. Furthermore, global and local EIS measurements were performed to distinguish between the cell voltage loss differences in the two cases. The mass transport losses η mtx and the Ohmic voltage losses η show a strong increase, when the stoichiometric water ratio falls below a level of λ ≈ 5. The reduction of the inlet water flux of the anode reduces both the proton conductivity of the ionomer within the catalyst layer and the membrane, increasing transport and Ohmic resistances, respectively. The local analysis has shown that the level of membrane and catalyst hydration under low stoichiometric conditions can be distributed highly non-homogeneous in along-the-channel direction, with the most pronounced dehydration toward the end of the channel.