Phosphonate-Based Metal–Organic Framework Derived Co–P–C Hybrid as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Abstract

Cobalt phosphate is considered to be one of the most active catalysts for the oxygen evolution reaction (OER) in neutral or near-neutral pH media, but only a few transition-metal phosphates are investigated in alkaline media, probably due to their poor intrinsic electrical conductivity and/or tendency to aggregate. Herein, in situ-formed cobalt phosphate decorated with N-doped graphitic carbon was prepared using phosphonate-based metal–organic frameworks (MOFs) as the precursor. It can serve as a highly active OER catalyst in alkaline media, affording a current density of 10 mA cm–2 at a small overpotential of 215 mV on the Ni foam. A combination of X-ray absorption spectroscopy and high-resolution XPS elucidates the origin of the high activity. Our observations unveil that cobalt diphosphate having the distorted metal coordination geometry with long Co–O and Co–Co distances is mainly responsible for the high OER activity. These results not only demonstrate the potential of a low-cost OER catalyst derived from phosphonate-based MOF but also open a promising avenue into the exploration of highly active and stable catalysts toward replacing noble metals as oxygen evolution electrocatalysts.

Orienting Active Crystal Planes of New Class Lacunaris Fe2PO5 Polyhedrons for Robust Water Oxidation in Alkaline and Neutral Media

“…As depicts in Figure S6c (Supporting Information), N‐Fe 2 PO 5– x polyhedrons exhibit much preferable electrocatalysis activity than Fe 3 N, suggesting the synergistic effect of nitrogen incorporation and phosphate group for expediting OER. The superior electrocatalysis capability of orthorhombic N‐Fe 2 PO 5– x ‐OT outperforms other state‐of‐the‐art metal phosphate‐based electrocatalysts in alkaline solution such as cobalt‐phytate, Ni 2 P 4 O 12 , cobalt phosphate, Co‐B i /GO, Co‐P‐C, and Ni 12 P 5 /Ni 3 (PO 4 ) 2 . Additionally, it is also better than other nonprecious metal‐based electrocatalysts such as Mn‐doped cobalt carbonate hydroxides, NiCo‐Se, NiFe‐LDH, FeOOH/Co/FeOOH, Ni‐Co nanowire, and NiFe‐P .…”

The Proportion of Fe‐NX, N Doping Species and Fe3C to Oxygen Catalytic Activity in Core‐Shell Fe‐N/C Electrocatalyst

“…The fitted N 1s spectrum reveals three peaks (Figure c), which are in accord with graphitic‐N, pyrrolic‐N, and pyridinic‐N, respectively, indicating successful doping of N element . Therein, pyridinic‐N (34.3 %) and graphitic‐N (34.8 %) are the dominant species (Table S1), which are generally considered as highly electroactive to endow the N doped carbon materials with efficient OER and ORR activities . Furthermore, the fitted Fe 2p spectrum is shown in Figure d. As a result, it is unsurprising that the metallic Fe is dominated in the Fe 2p spectrum with other chemical valence state.…”

“…[40] Therein, pyridinic-N (34.3 %) and graphitic-N (34.8 %) are the dominant species(Ta bleS1), which are generally considered as highly electroactive to endow the Nd oped carbon materials with efficient OER and ORR activities. [41,42] Furthermore, the fitted Fe 2p spectrumi ss hown in Figure 3d.A s ar esult, it is unsurprisingt hat the metallic Fe is dominated in the Fe 2p spectrum with other chemical valence state. The observed signal at 707.2 eV demonstrates the existence of Fe 3 C NPs.…”

Atomistic Investigation of Doping Effects on Electrocatalytic Properties of Cobalt Oxides for Water Oxidation

“…Although the thermodynamic benefits of this stronger hydrogen bonding formation cannot be expected for pristine Co oxide during the OOH* formation step, this finding suggests that the inherent local distortion of Fe eventually activates the bridge site by virtue of the strengthening of the hydrogen bond. A similar beneficial contribution of structural distortion to OER catalysis has also been observed for cobalt diphosphate, where the distorted metal coordination geometry was found to favor the water adsorption lowering the activation barrier of the OO bond formation …”