Hierarchical CoNiO2 Microflowers Assembled by Mesoporous Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction

Abstract

In order to alleviate the energy crisis and propel a low-carbon economy, hydrogen (H2) plays an important role as a renewable cleaning resource. To break the hydrogen evolution reaction (HER) bottleneck, we need high-efficiency electrocatalysts. Based on the synergistic effect between bimetallic oxides, hierarchical mesoporous CoNiO2 nanosheets can be fabricated. Combining physical representations with electrochemical measurements, the resultant CoNiO2 catalysts present the hierarchical microflowers morphology assembled by mesoporous nanosheets. The ultrathin two-dimensional nanosheets and porous surface characteristics provide the vast channels for electrolyte injection, thus endowing CoNiO2 the outstanding HER performance. The excellent performance with a fewer onset potential of 94 mV, a smaller overpotential at 10 mA cm−2, a lower Tafel slope of 109 mV dec−1 and better stability after 1000 cycles makes CoNiO2 better than that of metallic Co and metallic Ni.

Innovative Morphology Control Method: Modulating Metal Ratios in NixCoP@NF for Hydrogen Evolution Reaction

“…The exchange current density at different temperatures can be obtained from Tafel curves, as shown in Figure 7(b) (e), and it increases with temperature, consistent with the variation trend in the polarization curves. The electrochemical activation energy ( E a ) can be determined based on the Arrhenius equation, expressed as follows: log(j 0 )=logA‐ E a /2.303RT, where j 0 is the exchange current density obtained from the low overpotential range, and A is the Arrhenius constant [56] . The calculated results (Figure 7(c) (f)) show that the E a value of Ni 0.5 CoP@NF is significantly lower than that of the monometallic system CoP@NF and the rest of the Ni x CoP@NF samples with different doping ratios (Figure S7).…”

“…The electrochemical activation energy (E a ) can be determined based on the Arrhenius equation, expressed as follows: log(j 0 ) = logA-E a /2.303RT, where j 0 is the exchange current density obtained from the low overpotential range, and A is the Arrhenius constant. [56] The calculated results (Figure 7(c) (f)) show that the E a value of Ni 0.5 CoP@NF is significantly lower than that of the monometallic system CoP@NF and the rest of the Ni x CoP@NF samples with different doping ratios (Figure S7). This indicates that the appropriate Ni doping enhances the thermodynamics of the HER process, providing improved catalytic activity.…”