Shrinking the Hydrogen Overpotential of Cu by 1 V and Imparting Ultralow Charge Transfer Resistance for Enhanced H₂ Evolution

Abstract

Copper and its oxides are among the best electrocatalysts for the electrochemical conversion of CO 2 to value-added small organics because of its high hydrogen overvoltage, making the hydrogen evolution reaction (HER) a poor side reaction.Here we report an interesting finding that turned the nature of surface-oxidized Cu upside down in electrochemical H 2 evolution. It is commonly known that the electrochemical reactivity of a metal ion is highly sensitive to the anion to which it is coordinated in the electrolyte. In the case of Cu, when it is in the form of copper oxide, the hydrogen overvoltage is huge. Nonetheless, we found that when Cu is in coordination with Se 2− ions as Cu 2 Se, the hydrogen overvoltage was shrunken by ∼1 V, imparting ultralow charge transfer resistance (R CT ) that varied from 0.32 to 0.61 Ω depending on the means by which selenization was carried out. Selenization was done by two different methods. In one method, conventional stirring was employed to selenize Cu foam in a preheated NaHSe solution at 90 °C for 20 min. In another method, hydrothermal treatment was employed to selenize Cu foam with NaHSe solution at 120 °C for 1 h. The wetchemical method yielded honeycomb-like hierarchical arrays of Cu 2 Se sheets on Cu foam (designated as Cu 2 Se-ch/Cu), and the hydrothermal method yielded a uniform array of spiky rods of Cu 2 Se (designated as Cu 2 Se-ht/Cu). The HER electrocatalytic studies carried out in 0.5 M H 2 SO 4 showed that Cu 2 Se-ch/Cu and Cu 2 Se-ht/Cu had similar kinetics, with Tafel slopes of 32 to 35 mV dec −1 , which is closer to the state-of-the-art Pt/C. Interestingly, the Cu 2 Se-ch/Cu delivered a total kinetic current density of −1200 mA cm −2 when polarized up to −0.85 V vs RHE, whereas Cu 2 Se-ht/Cu delivered a maximum of −780 mA cm −2 only.

Air-stable phosphorus-doped molybdenum nitride for enhanced electrocatalytic hydrogen evolution

“…The referenced commercial Pt/C sample gives the smallest slope of 37 mV/dec, followed by P-Mo-N of 43 mV/dec, Mo-N of 76 mV/dec, and Mo 2 N-r of 71 mV/dec. A slope larger than 30 mV/dec for the P-Mo-N sample suggests a Volmer-Heyrovsky route for HER, 10,11,14 . The exchange current density (j 0 ), the most inherent measure of HER activity, was also calculated based on the Tafel equations (Supplementary Table 2).…”

“…Water electrolysis requires a stable electrocatalyst which has the ability to overcome high overpotential and provide efficient activity. To date, Pt-group materials are still the most commonly used catalysts in the commercial HER and there is a demand for a necessary replacement due to their limited supply and high cost [11][12][13][14][15][16][17][18][19][20] . For the sustainable and large-scale application of HER, earth-abundant materials have been under intense investigation in an effort to reach a suitable Pt-like HER performance [21][22][23][24][25][26][27][28][29][30] .…”

Appropriate Use of Electrochemical Impedance Spectroscopy in Water Splitting Electrocatalysis

“…To avoid this, several materials have been reported to be catalyzing these half‐cell reactions with relatively lower overpotentials. These include noble and precious metals (Pt, Ir, and Ru) and their oxides, non‐precious metals (Mn, Fe, Co, Ni, Cu, V, Ti, Mo, W, and Re) and their compounds and non‐metallic carbonaceous materials . Due to the cost concerns of utilizing noble and precious metals, non‐precious metals based materials are being investigated intensively for electrocatalytic water splitting in recent days.…”

Bio-Mediated Synthesis of Metal Nanomaterials for SERS Application

“…The presence of DNA in the aqueous and organosol results in an increase in stability and long-lasting property of the material [41,43]. Apart from the noble metals, we have also synthesized DNA templated chalcogenide materials such as CoS, CoSe, and NiTe, for water splitting electrocatalysis [45][46][47].…”