Bifunctional Electrocatalytic Behavior of Sodium Cobalt Phosphates in Alkaline Solution

Abstract

Noble-metal-free, bifunctional catalysts are essential to develop high-performance, cost-effective water-splitting systems. The current work explores the bifunctional electrocatalytic behavior of two sodium cobalt phosphate systems, namely, NaCoPO 4 and Na 2 CoP 2 O 7 , prepared by solution combustion synthesis (SCS) for the first time. Formation of phase-pure orthorhombic maricite NaCoPO 4 (space group: Pnma) and orthorhombic Na 2 CoP 2 O 7 (space group: Pna2 1 ) was confirmed by Rietveld refinement. The electrocatalytic activity of maricite NaCoPO 4 and Na 2 CoP 2 O 7 was investigated by using linear sweep voltammetry with a rotating disk electrode (RDE). The oxygen reduction reaction (ORR) activities of these sodium cobalt phosphates are comparable to Vulcan carbon black and Pt/C. Oxygen evolution reaction (OER) activity of Na 2 CoP 2 O 7 is dominant compared to NaCoPO 4 and Pt/C. The Tafel slope, electron-transfer number, and stability of the sodium-metal phosphates were calculated in different concentrations of Na + -containing aqueous electrolyte. The bifunctional activity and good stability of the sodium cobalt phosphates stem from cobalt ions and stabilization of the catalytic centers by the phosphate frameworks. The present work demonstrates sodium cobalt phosphates as alternate costeffective, novel electrocatalysts for efficient OER/ORR activity in alkaline solution.

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

“…The superior ORR activity of NaFePO 4 could be attributed to the stabilization of active (Fe II ) centers by the phosphate framework, which thereby facilitates oxygen binding with the (Fe II ) centers . In addition, the conductive carbon coating wrapped around the particles and orthorhombic crystal structure of maricite NaFePO 4 favors its ORR activity compared with that of monoclinic KFePO 4 …”

Sodium Cobalt Metaphosphate as an Efficient Oxygen Evolution Reaction Catalyst in Alkaline Solution

“…The corresponding pore size distribution curves are shown for NCoM-Cb-Ar and NCoM-Cb-Air in Figure S10. [11] The drop in OER current density at 1.758 V for NCoM-SS-Ar (18 %) catalyst during the stability test was smaller than that of NCoM-SS-Air (73 %) (Figures 4 d and 4c, respectively). [28] The electrocatalytic activity of cobalt-based metaphosphates is shown in Figure 3.…”

“…[3] As a result of their excellent electrochemical performance and versatile structure, phosphate-based polyanionic materials have offered a range of promising electrodes for Li-ion batteries (LIBs) and Na-ion batteries (SIBs). These electrocatalysts are based on abundant 3d transition-metal ( T M) incorporated inside the lattice as oxides, [6] hydroxides, [7] perovskites, [8] phosphides, [9] chalcogenides, [10] phosphates, [11] molecular compounds, [12] and as oxides decorated on graphene. These electrocatalysts are based on abundant 3d transition-metal ( T M) incorporated inside the lattice as oxides, [6] hydroxides, [7] perovskites, [8] phosphides, [9] chalcogenides, [10] phosphates, [11] molecular compounds, [12] and as oxides decorated on graphene.…”

Phosphate‐Based Electrocatalysts for Water Splitting: Recent Progress

“…It is still a challenge to explore a facile and efficient way in the manufacture of catalyst with superior water oxidation performance. New techniques are carried out to provide more synthetic methods for catalysts such as in situ surface derivation, electrochemical topotactic conversion or oxidative polarization, solid‐state method, sol‐gel method, solution combustion synthesis (SCS) and chemical vapor deposition (CVD) and microwave‐assisted method ,. For example, CCH@Co−Pi NA/Ti was obtained via in situ electrochemical surface derivation used Co(CO 3 ) 0.5 (OH) ⋅ 0.11H 2 O nanoarray on Ti mesh (CCH NA/Ti) as the precursor .…”