Advanced catalyst materials for water splitting are central for the progress of clean and renewable energy sources.

Among various methods available for water splitting, thermal, electrochemical and photochemical approaches have attained enormous research owing to the zero-emission, high energy density and conversion efficiencies. Water splitting via the electrochemical route is governed by two half-cell reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), in which the OER is energetically challenging owing to sluggish electrode kinetics.

Present works mainly aim at decreasing the overpotential and improving the energy conversion efficiency of various electrocatalysts used in water splitting reactions. So far, platinum and their compounds are regarded as state-of-the art electrocatalyst owing to their high efficiencies, while the scarcity and high cost has restricted the advancement in this field and subsequently prompt explorations for economically viable alternatives.

So far, nickel and their derivatives, such as nickel-alloys, raney nickel and so-on, were used as traditional electrocatalysts for alkaline water-electrolysis. However, the research on catalyst materials progressed so rapidly onto other classes of materials, such as oxides, hydroxides, phosphides and chalcogenide based nanostructured materials due to their high catalytic activities and abundance.

However the choice of the electrocatalyst depends upon vital parameters such as high specific surface area, good porosity, high electronic conductivity, substantial electroactive sites, low electronegativity, low band gap, structural diversity, chemical stability and the better band alignment with water redox levels for higher catalytic efficiencies. 

Proton-exchange-membrane (PEM) electrolyzers employ different classes of platinum based catalysts ranging from platinum black to carbon supported platinum catalysts. Platinum black catalysts are not economically feasible due to their low surface areas, requiring the use of higher platinum loadings per unit area in order to attain reasonable performance.

Platinum on carbon (Pt/C) catalysts have higher active surface areas and are the materials of choice in today’s fuel cells. Pt/C catalysts are now available in different platinum loading amounts. Very recently platinum-transition metal alloys loaded on carbon (Pt-X/C), have shown two to four fold increase in the performance of PEM electrolyzers. 

Solid oxide electrolyzer cell (SOEC) generally employ asymmetric materials for cathode and anode. Traditionally nickel doped Yttria-stabilized zirconia has been used as a cathode and Lanthanum strontium manganate in the most commonly used anode.

However, there are several reports on the degradation of the catalyst materials and also the re-oxidation of nickel to nickel oxide. Furthermore, various alternative combinations of materials are currently under investigation by different research groups. 

Choice of the catalyst material plays a pivotal role in the manufacturing of the electrolyzers of the desired performance.

At Newtrace, we employ cost-effective, rare-earth free and non-platinum group elements for the design and development of the electrocatalysts. 

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References: 

1. He et al., 2005, Electrochem. Soc. Interface, 14 41. 
2. M.A. Laguna-Bercero, 2012, Journal of Power Sources, 203, 4-16.
3. H. Uchida et al., 2004,  Electrochem. Solid State Lett., 7, A500–A502.

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