Abstract
The observation of extraordinarily high conductivity in delafossite-type PdCoO2 is of great current interest, and there is some evidence that electrons behave like a fluid when flowing in bulk crystals of PdCoO2. Thus, this material is an ideal platform for the study of the electron transfer processes in heterogeneous reactions. Here, we report the use of bulk single-crystal PdCoO2 as a promising electrocatalyst for hydrogen evolution reactions (HERs). An overpotential of only 31 mV results in a current density of 10 mA cm–2, accompanied by high long-term stability. We have precisely determined that the crystal surface structure is modified after electrochemical activation with the formation of strained Pd nanoclusters in the surface layer. These nanoclusters exhibit reversible hydrogen sorption and desorption, creating more active sites for hydrogen access. The bulk PdCoO2 single crystal with ultrahigh conductivity, which acts as a natural substrate for the Pd nanoclusters, provides a high-speed channel for electron transfer.
Highlights
Delafossite-type metals such as PdCoO2 are currently attracting considerable attention due to their exotic and surprising physical properties
Further investigation of the hydrogen evolution reactions (HERs) process revealed that two electron transfer processes are involved
What is the HER performance of a bulk single crystal with strikingly low roomtemperature resistivity? Can we combine the characteristics of high current density, low Tafel slope and high electrochemical stability in a single compound?
Summary
Catalyst for hydrogen evolution reaction (HER) has a large exchange current density, a low Tafel slope, and high electrochemical stability. The intensity of the LF semicircle decreases and shifts to a higher frequency, indicating an increase in the reaction rate and a shorter reaction time constant (τ = 1/ωp, where τ is the time constant and ωp is the characteristic frequency).[41,42] In contrast, the time constant at HF has a slight decrease in density and is much lower than the HER kinetics value This corresponds to the response of a fast electron transfer process, as proposed by Omanovic et al.[43] we can conclude that the high electrical conductivity of the PdCoO2 single crystal is of great importance for electron injection onto the catalyst surface.
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