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

Copper and its oxides are among the best electrocatalysts for the electrochemical conversion of CO₂ 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 H₂ 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 Cu₂Se, the hydrogen overvoltage was shrunken by ∼1 V, imparting ultralow charge transfer resistance (<i>R</i>_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 wet-chemical method yielded honeycomb-like hierarchical arrays of Cu₂Se sheets on Cu foam (designated as Cu₂Se-ch/Cu), and the hydrothermal method yielded a uniform array of spiky rods of Cu₂Se (designated as Cu₂Se-ht/Cu). The HER electrocatalytic studies carried out in 0.5 M H₂SO₄ showed that Cu₂Se-ch/Cu and Cu₂Se-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 Cu₂Se-ch/Cu delivered a total kinetic current density of −1200 mA cm^–2 when polarized up to −0.85 V vs RHE, whereas Cu₂Se-ht/Cu delivered a maximum of −780 mA cm^–2 only

Stainless Steel Scrubber: A Cost Efficient Catalytic Electrode for Full Water Splitting in Alkaline Medium

Sometimes, searching for a cost efficient bifunctional catalytic material for water splitting can be accomplished from a very unlikely place. In this work, we are reporting such a discovery of utilizing the stainless steel (SS) scrubber directly as a catalytic electrode for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of water electrolysis in 1 M KOH. The <i>iR</i> corrected overpotential calculated at an areal current density of 10 mA cm^–2 for a SS scrubber in HER is 315 mV which is 273 mV higher than Pt/C. Similarly, the SS scrubber required 418 mV at 10 mA cm^–2 which is just 37 and 98 mV higher than Ni­(OH)₂ and RuO₂. Interestingly, the kinetic analysis revealed that the SS scrubber had facile kinetics for both HER and OER in 1 M KOH as reflected by their corresponding Tafel slope values viz., 121 and 63 mV dec^–1, respectively. In addition, the two electrode cell fabricated using the same SS scrubber electrode delivered 10 mA cm^–2 at 1.98 V. Beyond everything, the SS scrubber had shown ultrahigh stability in both half-cell and full-cell studies for total water splitting. Further, as far as the cost of an electrode material per gram is concerned, the SS scrubber defeats all the best electrocatalysts of water splitting by having a price of just $0.012 USD which is$2.228 USD lower than pure Ni, $59.658 USD lower than RuO₂ and$158.028 USD lower than Pt/C 20 wt % catalyst. The overall study specified that the SS scrubber can be adapted for cost-efficient large scale water electrolysis for bulk hydrogen production