The thermodynamics and electronic structure analysis of P-doped spinel Co3O4

Unveiling Surface Species Formed on Ni-Fe Spinel Oxides During the Oxygen Evolution Reaction at the Atomic Scale

Optimizing electrocatalyst performance requires an atomic-scale understanding of surface state changes and how those changes affect activity and stability during the reaction. This is particularly important for the oxygen evolution reaction (OER) since the electrocatalytically active surfaces undergo substantial reconstruction and transformation. Herein, a multimodal method is employed that combines X-ray photoemission spectroscopy, transmission electron microscopy, atom probe tomography, operando surface-enhanced Raman spectroscopy with electrochemical measurements to examine the surface species formed on NiFe2O4, P-doped NiFe2O4 and Ni1.5Fe1.5O4 upon OER cycling. The activated NiFe2O4 and P-doped NiFe2O4 exhibit a significantly lower Tafel slope (≈40 mV dec-1) than Ni1.5Fe1.5O4 (≈90 mV dec-1), although oxyhydroxides are grown on all three Ni-Fe spinels during OER. This is likely attributed to the formation of a ≈1 nm highly defective layer with a higher oxygen concentration on the activated NiFe2O4 and P-doped NiFe2O4 nanoparticle surfaces (than that in bulk), which improves the charge transfer kinetics toward OER. Such surface species are not formed on Ni1.5Fe1.5O4. Overall, this study provides a mechanistic understanding of the role of Fe, P, and Ni in forming active oxygen species in the Ni-based spinels toward OER.

Cold plasma synthesis of phosphorus-doped CoFe2O4 with oxygen vacancies for enhanced OER activity

Spinel-type metal oxides are promising electrocatalysts for the oxygen evolution reaction (OER) due to their unique electronic structure and low cost. Herein, we induced oxygen vacancies and doped phosphorus into CoFe2O4 using cold plasma. The abundant oxygen vacancies enhanced hydrophilicity and modified the electronic structure of CoFe2O4, while the phosphorus doping formed numerous new active centers. The doped P and formed FeP promoted the charge transfer and improved the conductivity of the catalyst. The phosphorus-doped CoFe2O4 exhibited exceptional OER activity with an overpotential of 180 mV at 10 mA cm-2 and a Tafel slope of 65.8 mV dec-1 in an alkaline electrolyte. DFT calculations confirmed that phosphorus doping can improve the charge distribution near the Fermi level and optimize the d-band center position.

Synthesis of methyl glycolate by hydrogenation of dimethyl oxalate with a P modified Co/SiO2 catalyst

A P-modified Co/SiO₂ catalyst was reported for the first time in the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) reaction and the synthesized Co₈P/SiO₂ exhibited 94.6% conversion of DMO and 88.1% selectivity to MG during a 300 h continuous test. The doping element of P in the catalyst was indispensable and played an important role in improving the catalytic performance of the Co/SiO₂ catalyst.