Developing highly efficient and affordable noblemetal-free catalysts toward the hydrogen evolution reaction (HER) is an important step toward the economical production of hydrogen. As a nonprecious-metal catalyst for the HER, molybdenum nitride (MoN) has excellent corrosion resistance and high electrical conductivity, but its catalytic activity is still inadequate. Here we report our findings in dramatically enhancing the HER activity of MoN by creating porous MoN@nitrogendoped carbon (MoN-NC) nano-octahedrons derived from metal−organic frameworks (MOFs). The composite catalyst displays remarkably high catalytic activity, demonstrating a low overpotential of 62 mV at a current density of 10 mA cm −2 (η 10 ), a small Tafel slope of 54 mV dec −1 , and a large exchange current density of 0.778 mA cm −2 while maintaining good stability. The enhancement in catalytic properties is attributed to the unique nanostructure of the MoN, the high porosity of the electrode, and the synergistic effect between the MoN and the nitrogendoped carbon substrate. The performances are among the best ever reported for nonprecious-metal-based electrocatalysts (comparable to those of a 20% Pt/C commercial catalyst), making the porous MoN-NC nano-octahedrons some of the most active and acid-stable electrocatalysts for the HER.

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A solid oxide fuel cell (SOFC) is a highly efficient device for converting chemical energy to electrical energy. In addition to the efforts to reduce the operating temperature of SOFCs to below 600 °C, research studies of the basic mechanism of CO2 poisoning on cathode materials are envisioned to improve the operation of dual-chamber SOFCs using ambient air. In this work, we comparatively studied the CO2 poisoning effect on two highly active perovskites SrSc(0.175)Nb(0.025)Co(0.8)O(3-δ) (SSNC) and Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF), using complementary characterization techniques, e.g., powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), CO2-temperature-programmed desorption (CO2-TPD), and electrochemical impedance spectroscopy (EIS). The SSNC cathode shows better tolerance to CO2 as compared with BSCF, which is attributed to the absence of Ba, higher average metal-oxygen bond energy (ABE) of SSNC, and the higher acidity of Nb(5+) cations, whereas the oxygen vacancy concentration plays a less important role.

A novel strategy to tweak the oxygen evolution activity of nanofilms by exploiting the film-substrate redox interaction.