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The Performance of Nickel and Nickel-Iron Catalysts Evaluated As Anodes in Anion Exchange Membrane Water Electrolysis

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The Performance of Nickel and Nickel-Iron Catalysts Evaluated As Anodes in Anion Exchange Membrane Water Electrolysis catalysts Article The Performance of Nickel and Nickel-Iron Catalysts Evaluated As Anodes in Anion Exchange Membrane Water Electrolysis Emily Cossar 1, Alejandro Oyarce Barnett 2,3,*, Frode Seland 4 and Elena A. Baranova 1,* 1 Department of Chemical and Biological Engineering, Centre for Catalysis Research and Innovation (CCRI), University of Ottawa, 161 Louis-Pasteur Ottawa, ON K1N 6N5, Canada; [email protected] 2 SINTEF Industry, Sustainable Energy Technology Department, New Energy Solutions Group, NO-7491 Trondheim, Norway 3 Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway 4 Department of Materials Science and Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway; [email protected] * Correspondence: [email protected] (A.O.B.); [email protected] (E.A.B.); Tel.: +47-9300-3263 (A.O.B.); +(613)-562-5800 (ext. 6302) (E.A.B.) Received: 29 August 2019; Accepted: 24 September 2019; Published: 27 September 2019 Abstract: Anion exchange membrane water electrolysis (AEMWE) is an efficient, cost-effective solution to renewable energy storage. The process includes oxygen and hydrogen evolution reactions (OER and HER); the OER is kinetically unfavourable. Studies have shown that nickel (Ni)- iron (Fe) catalysts enhance activity towards OER, and cerium oxide (CeO2) supports have shown positive effects on catalytic performance. This study covers the preliminary evaluation of Ni, Ni90Fe10 (at%) and Ni90Fe10/CeO2 (50 wt%) nanoparticles (NPs), synthesized by chemical reduction, as OER catalysts in AEMWE using commercial membranes. Transmission electron microscopy (TEM) images of the Ni-based NPs indicate NPs roughly 4–6 nm in size. Three-electrode cell measurements indicate that Ni90Fe10 is the most active non-noble metal catalyst in 1 and 0.1 M KOH. AEMWE measurements of 2 the anodes show cells achieving overall cell voltages between 1.85 and 1.90 V at 2 A cm− in 1 M KOH at 50 ◦C, which is comparable to the selected iridium-black reference catalyst. In 0.1 M KOH, 2 the AEMWE cell containing Ni90Fe10 attained the lowest voltage of 1.99 V at 2 A cm− . Electrochemical impedance spectroscopy (EIS) of the AEMWE cells using Ni90Fe10/CeO2 showed a higher ohmic resistance than all catalysts, indicating the need for support optimization. Keywords: nickel; iron; ceria; OER; alkaline exchange membrane; electrolysis; anode 1. Introduction As global warming and climate change concerns continue to rise, the concept of a “hydrogen economy” is becoming more and more important. This ideal is based on using hydrogen (H2) as a clean, renewable fuel [1]. H2 can also be used to store renewable energy through water electrolysis [2]. Water electrolysis utilizing anion exchange membranes (AEMs) is an emerging water electrolysis technology, used for its ability to produce hydrogen both efficiently and at low cost. Compared to traditional alkaline water electrolysis, which employ porous diaphragm separators, solid polymer electrolytes may provide certain advantages, such as lower gas crossover, improved efficiency, higher current densities, differential pressure operation and improved operation dynamics [3]. Unlike other solid polymer electrolyser technologies, such as proton exchange membrane water electrolysis (PEMWE), anion exchange membrane water electrolysis (AEMWE) technology has the potential to Catalysts 2019, 9, 814; doi:10.3390/catal9100814 www.mdpi.com/journal/catalysts Catalysts 2019, 9, 814 2 of 17 Catalysts 2019, 9, x FOR PEER REVIEW 2 of 17 operate without expensive noble-metal catalysts, such as iridium, ruthenium and platinum, in addition 45 toplatinum, low-cost materials in addition for bipolarto low- platescost materials and current for collectors.bipolar plates AEMWE, and therefore,current collectors. aims to combine AEMWE, 46 thetherefore, low costs aims of alkaline to combine electrolysis the low costs with of the alkaline high e ffielectrolysisciency and with flexibility the high of efficiency the proton and exchange flexibility 47 membraneof the proton (PEM) exchange electrolysis membrane design (PEM) [3]. electrolysis design [3]. 48 TheThe theoretical theoretical thermodynamic thermodynamic potential potential for fo waterr water electrolysis electrolysis is is 1.23 1.23 V V at at room room temperature. temperature. 49 ToTo achieve achieve a lowa low activation activation overvoltage overvoltage during during electrolysis’s electrolysis’s operation, operation, high high performing performing oxygen oxygen and and 50 hydrogenhydrogen evolving evolving catalysts catalysts are are required. required. As As the the goal goal of of water water electrolysis electrolysis is is its its industrialization, industrialization, 51 catalystcatalyst cost cost is imperative.is imperative. As As such, such, the the development development of of active active non-noble non-noble metal metal catalysts catalysts is is crucial crucial to to 52 furtherfurther develop develop and and establish establish AEMWE AEMWE technology. technology The. The number number of of studies studies addressing addressing performance performance 53 improvementsimprovements through through the the development development of of new new AEM AEM materials, materials, catalysts catalysts and and membrane membrane electrode electrode 54 assembliesassemblies (MEAs) (MEAs) have have increased increased in in recent recent years years [4 –[413–].13]. However, However, the the water water splitting splitting performance performance 55 reportedreported for for AEMWE AEMWE is still is still lower lower than than that ofthat PEMWE of PEMWE [14,15 [14,15],], particularly particularly when employingwhen employing non-noble non- 56 metalnoble catalysts metal catalysts and lower and concentrations lower concentrations of alkaline of solutions,alkaline solutions, or water or [16 water]. [16]. 57 TheThe water water electrolysis electrolysis process process occurs occurs through through two two simultaneously simultaneously occurring occurring half-cell half-cell reactions: reactions: 58 thethe oxygen oxygen evolution evolution reaction reaction (OER) (OER) on on the the anode anode and and the the hydrogen hydrogen evolution evolution reaction reaction (HER) (HER) on on the the 59 cathode.cathode. OER OER kinetics kinetics are are more more sluggish sluggish than than HER HER kinetics kinetics [17 [17];]; therefore, therefore, the the performance performance of of water water 60 electrolyserselectrolysers heavily heavily depends depends on on the the OER. OER. Generally, Generally, the the OER OER activity activity of non-noble of non-noble electrocatalysts electrocatalysts is 61 highis high in alkaline in alkaline environments environments [14]. [14]. Non-noble Non-noble metal metal oxides oxides are, therefore,are, therefore, of interest of interest as catalysts as catalysts for 62 AEMWE.for AEMWE. More specifically,More specifically, catalysts catalysts based on based Ni or Coon (hydroxides, Ni or Co (hydroxides, oxides, spinels oxides, and perovskites) spinels and 63 andperovskites) pyrochlores and show pyrochlores good activity show towards good activity the OER towards in alkaline the media.OER in Ni-based alkaline electrocatalystsmedia. Ni-based 64 haveelectrocatalysts been particularly have wellbeen investigated,particularly well and investigated, include different and ratiosinclude of different Ni–iron (Fe),ratios Ni–chromium of Ni–iron (Fe), 65 (Cr)Ni– andchromium Ni–molybdenum (Cr) and Ni (Mo)–molybdenum oxide catalysts (Mo) oxide [6,18– 23catalysts], amongst [6,18– other23], amongst bimetallics other and bimetallics alloys. 66 Liand et al. alloys. [18] studied Li et alvarious. [18] studied electrodeposited, various electrodeposited, Ni-bimetallic catalysts Ni-bimetallic for OER. catalysts Among for all OER. tested Among metals, all 67 thetested NiFe catalystmetals, showedthe NiFe the catalyst highest promotionalshowed the effhighestect, achieving promotional the lowest effect, overpotential achieving ofthe 256 lowest mV 2 68 atoverpotential 0.5 A cm− with of 10%256 mV iron at incorporation. 0.5 A cm-2 with Similarly, 10% iron Trotochaud incorporation. et al. [Similarly,20] tested Trotochaud multiple metal et al and. [20] 69 mixed-metaltested multiple oxide metal catalysts and preparedmixed-metal by spin oxide coating catalyst fors OER. prepared Their by study spin showed coating thatfor OER. the Ni Their90Fe10 studyOx 2 70 catalystshowed obtained that the the Ni lowest90Fe10Ox overpotential catalyst obtained of 297 the mV lowest at 1 mA overpotential cm− . of 297 mV at 1 mA cm-2. 71 TheThe most most widely widely accepted accepted description description of of the the Ni Ni oxidation oxidation steps steps in in alkaline alkaline media media is is through through the the 72 BodeBode diagram, diagram, a simplifieda simplified version version of of which which is shownis shown in in Figure Figure1 below 1 below [24 ].[24]. charge Ni α-Ni(OH) γ-NiOOH 2 discharge aging overcharge charge β-Ni(OH) β-NiOOH 2 discharge 73 Figure 1. Nickel oxidation steps in alkaline media. 74 Figure 1. Nickel oxidation steps in alkaline media. In an alkaline environment, nickel is first oxidized to the unstable α-Ni(OH) (about 0.5 V versus 2 − 75 Hg/HgO).In an Prolonged alkaline exposureenvironment, to an alkalinenickel is environment first oxidized or slightto the anodic unstable polarization α-Ni(OH) brings2 (about it to –0.5 the V 76 stableversusβ-Ni(OH) Hg/HgO).2 phase. Prolonged Further
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