Highly efficient and stable electrocatalysts, particularly those that are capable of multifunctionality in the same electrolyte, are in high demand for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this work, highly monodisperse CoP and Co2P nanocrystals (NCs) are synthesized using a robust solution‐phase method. The highly exposed (211) crystal plane and abundant surface phosphide atoms make the CoP NCs efficient catalysts toward ORR and HER, while metal‐rich Co2P NCs show higher OER performance owing to easier formation of plentiful Co2P@COOH heterojunctions. Density functional theory calculation results indicate that the desorption of OH* from cobalt sites is the rate‐limiting step for both CoP and Co2P in ORR and that the high content of phosphide can lower the reaction barrier. A water electrolyzer constructed with a CoP NC cathode and a Co2P NC anode can achieve a current density of 10 mA cm−2at 1.56 V, comparable even to the noble metal‐based Pt/C and RuO2/C pair. Furthermore, the CoP NCs are employed as an air cathode in a primary zinc–air battery, exhibiting a high power density of 62 mW cm−2and good stability.
The application of Co2‐xRhxP nanoparticles as electrocatalysts for the hydrogen evolution reaction (HER) and overall water splitting in basic media is reported. The experimental design seeks to dilute rhodium with earth‐abundant cobalt as a means to lower the cost of the material and achieve catalytic synergism, as reported for related bimetallic phosphides. The HER activity of Co2‐xRhxP is found to be composition‐dependent, with the rhodium‐rich compositions being more active as compared to their cobalt‐rich counterparts, with overpotentials (η) at 10 mA/cm2geometricof 58.1–63.9 mV vs. 82.1–188.1 mV, respectively. In contrast, Co‐rich Co2‐xRhxP nanoparticles are active for the oxygen evolution reaction (OER) process in basic media, with η= 290 mV for x=0.25. A full water electrolysis cell was created using the most active compositions for OER and HER as the anode and cathode, respectively, generating an overall η= 390 mV. Notably, the cell became more active over a 50 h stability test, increasing by 2 mV/cm2geometricat a constant applied voltage of 1.62 V vs NHE. This enhanced activity correlates with nanoscale phase segregation of Rh in the anode. Thus, the lower overpotential achieved for Co1.75Rh0.25P relative to Co2P, and the augmented activity over time in the former, may be a consequence of restructuring of the anode driven by Rh phase‐segregation. The augmentation in activity at the anode more than compensates for small losses at the cathode.
more » « less- Award ID(s):
- 1904775
- NSF-PAR ID:
- 10288054
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemCatChem
- Volume:
- 13
- Issue:
- 19
- ISSN:
- 1867-3880
- Page Range / eLocation ID:
- p. 4111-4119
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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