Autologous Cobalt Phosphates with Modulated Coordination Sites for Electrocatalytic Water Oxidation

Abstract

The correlation between metal coordination and electrocatalytic water oxidation performance is elusive in many cobalt-based materials. Herein, we designed an ideal Co phosphate-based platform to explore the effect of coordination environment on oxygen evolution reaction (OER) activity. The cobalt geometry was modulated from octahedral to tetrahedral by simple removal of water ligands in Co 3 (PO 4 ) 2 ·8 H 2 O. Other features except the coordination structure in the two autologous materials remain similar. The two analogues display the same OER kinetics, but the anhydrous Co 3 (PO 4 ) 2 exhibits a greatly enhanced OER activity. On the basis of Raman and operando XAS results, the higher intrinsic activity of the Co tetrahedral sites is because they facilitate the formation of active high valent cobalt (hydr)oxide intermediates during OER. This work not only brings insights of OER on Co-based electrocatalysts but also provides a reference system to study the effect of metal geometry on electrocatalysis.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Figure 3. a) CVs, b) Tafel plots based on kinetic currents, c) DPV curves of the Co 3 (PO 4 ) 2 ·8 H 2 O and Co 3 (PO 4 ) 2 . The electrochemical response of d) Co 3 (PO 4 ) 2 and e) Co 3 (PO 4 ) 2 ·8 H 2 O in electrolytes with different pH values. f) The linear plots of the pre-catalytic oxidation potentials and the kinetic catalytic currents against the pH values of the electrolytes (colours as in a-c).

Comprehensive Understandings into Complete Reconstruction of Precatalysts: Synthesis, Applications, and Characterizations

“…realized the transformation of cobalt phosphate from octahedron to tetrahedron by dehydration at high‐temperature treatment. [ 119 ] The electrocatalytic results showed that Co 3 (PO 4 ) 2 with cobalt tetrahedron had higher activity than that of Co 3 (PO 4 ) 2 ·8H 2 O with cobalt octahedron, which was attributed to that Co tetrahedral site could promote the formation of high‐valent cobalt active species in OER. Besides, the phosphate group has also been confirmed to be proton acceptors and can induce distorted local structure, and thus is conducive to water adsorption and catalytic oxidation.…”

Design Strategies of Transition‐Metal Phosphate and Phosphonate Electrocatalysts for Energy‐Related Reactions

“…Density functional theory calculations revealed that Na 2 CoP 2 O 7 had low energy barrier and the OER pathway in Na 2 CoP 2 O 7 used 4‐ and 5‐coordinated cobalt atoms stabilized by actively rotating pyrophosphate groups. Moreover, further studies indicate the higher intrinsic activity from Co tetrahedral sites is their facilitation on forming active high valent cobalt (hydro)oxide intermediates during OER [39] . Additionally, it has been reported NaCo 4 (PO 4 ) 3 with 5‐coordinations have better OER catalytic performance in neutral solution compared with Na 2 CoP 2 O 7 with 4‐coordinated Co configurations [40] …”

Rational Construction of a N, F Co‐doped Mesoporous Cobalt Phosphate with Rich‐Oxygen Vacancies for Oxygen Evolution Reaction and Supercapacitors

“…Inorganic porous materials display interesting physical properties, such as magnetic, heterogeneous catalysis, adsorption/separation, and ion‐exchange due to their diverse composition of metal ions and unique porous structure [1–9] . Among them, porous transition‐metal phosphates have been attracting wide attention in renewable energy conversion and storage technology, [2,3] such as supercapacitors, [10,11] metal‐air batteries, especially, hydrogen energy from water splitting [2,12–16] . However, the overpotential at 10 mA/cm 2 for oxygen evolution reaction (OER) in the process of water splitting, corresponding to 10 % solar‐to‐fuel conversion efficiency, is still significantly higher than the standard potential of ∼1.23 V because it involves multiple proton‐coupled electron transfers (PCET) process, leading to its sluggish kinetics.…”

“…[1][2][3][4][5][6][7][8][9] Among them, porous transition-metal phosphates have been attracting wide attention in renewable energy conversion and storage technology, [2,3] such as supercapacitors, [10,11] metal-air batteries, especially, hydrogen energy from water splitting. [2,[12][13][14][15][16] However, the overpotential at 10 mA/cm 2 for oxygen evolution reaction (OER) in the process of water splitting, corresponding to 10 % solar-to-fuel conversion efficiency, is still significantly higher than the standard potential of~1.23 V because it involves multiple proton-coupled electron transfers (PCET) process, leading to its sluggish kinetics. Many electrocatalysts such as metal-based oxysalts: oxides/hydroxides, [8] phosphates and borates, [2,3] especially, porous transition-metal phosphates with H 2 PO 4 À or HPO 4 2À unique proton acceptors, have shown superb electrocatalytic performance toward OER in local pH environment, thus, they have been widely used as promising candidates owing to their various metal coordination configuration and structural stability.…”