Earth‐Abundant Alkali Iron Phosphates (AFePO₄) as Efficient Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Solution

Abstract

Water‐splitting systems are essential for clean energy production. The oxygen reduction reaction (ORR) is a key reaction involved in water splitting, which requires a catalyst. The current work explores the possible application of sodium and potassium iron phosphates (AFePO4, A=Na and K) as electrocatalysts for ORR activity. These earth‐abundant iron phosphates were synthesized by the solution combustion synthesis (SCS) technique by using ascorbic acid both as fuel and reducing agent for Fe. The crystal structure was analyzed by Rietveld refinement. The formation of carbon coating was identified by thermogravimetric analysis and Raman spectroscopy. Electrocatalytic properties of AFePO4 were investigated in alkali electrolytes for the first time by using linear sweep voltammetry with a rotating disk electrode (RDE). The ORR activities of these alkali iron phosphates are comparable to that of the Pt/C system. The Tafel slope and electron transfer number of the alkali iron phosphates were calculated. The ORR activity of NaFePO4 was found to be better than KFePO4 and FePO4. This work demonstrates alkali iron phosphates as alternate cost‐effective, novel electrocatalysts for productive ORR activity in alkaline solution.

Nitrogen-Doped Porous Carbon Derived from Biomass Used as Trifunctional Electrocatalyst toward Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions

“…Hence, researchers have aimed to replace those aforementioned noble electrocatalysts by low-cost, large surface area and earth-abundant materials for ORRs, HERs and OERs [16]. On the other hand, non-noble materials such as metal oxides (α-Fe 2 O 3 , Co 3 O 4 /C and Mn 3 O 4 ), metal phosphates (Co, Fe, Ni and Mn) and dichalcogenides (MoS 2 and CoS 2 ), have been investigated as electrocatalysts in ORRs, OERs and HERs [17][18][19][20][21][22]. Still, these catalysts have the disadvantages of toxic precursor materials, and the production of toxic wastes in the form of hydroxides, oxides and metal complexes.…”

Nickel Cobalt Phosphite Nanorods Decorated with Carbon Nanotubes as Bifunctional Electrocatalysts in Alkaline Medium with a High Yield of Hydrogen Peroxide

“…The peak at 870 cm −1 may be assigned to H−P−O vibration. The peaks in the range 600–200 cm −1 correspond to coupled effect of lattice modes of −PO 3 H, CoO 6 and NiO 6 due to the extended network of the microporous crystal structure . The peaks at 489 and 578 cm −1 may be assigned to the −PO 3 deformations .…”

“…Hence, alternative low cost and earth abundant catalysts based on non‐precious transition metal oxides and hydroxides (Ni(OH) 2 , Co(OH) 2 , MoO 2 , MoO 3, WO 3 , etc.) and dichalcogenides MoS 2 , CoS 2 are explored for electrocatalysis . Recently, transition metal salts of phosphorous oxy acids have gained more attention towards electrocatalytic applications due to their earth abundance, low cost, environmentally benign nature and high efficiency.…”

Mn3+ Active Surface Site Enriched Manganese Phosphate Nano‐polyhedrons for Enhanced Bifunctional Oxygen Electrocatalyst

“…Moreover, the electron transfer from Mn 3+ to the absorbed O 2(ad) species is a vital step in the Mn‐based ORR catalysts which gives rise to the formation of Mn 4+ ‐O 2‐(ad) , which in turn depends on the Mn 3+/ Mn 4+ ratio at the surfaces. Hence, it is highly anticipated that Mn 3+ is the most favorable for higher bifunctional catalytic activity due to the ease of oxidation to Mn 4+ state . It has also been confirmed in Mn−Co spinel oxide compounds that those having largest ratio of Mn 4+ /Mn 3+ has the highest ORR activity .…”