Cu₂O−Cu₂Se Mixed‐Phase Nanoflake Arrays: pH‐Universal Hydrogen Evolution Reactions with Ultralow Overpotential

Abstract

Most developed hydrogen evolution reaction (HER) electrocatalysts have pH-dependent functionalities, which limit their universal applications. Pt, the ideal HER electrocatalyst, is also highly effective in specific pH conditions. In the present article, we report a copper-based transition-metal chalcogenide from anion engineering. Hierarchical three-dimensional (3D) Cu 2 OÀ Cu 2 Se nanoflake arrays (COCS NFs) are grown directly on nickel foam (NF) by combining the rapid electrodeposition technique with the room temperature wet-chemical selenization method. Via the synergetic effects of the proper ratio of Se and O, as-synthesized COCS NFs manage to accomplish keyrequirements for pH-universal HER performances with overpotential values of 52.9, 62.8, and 77.8 mV, in alkaline, neutral, and acidic media, respectively, at 10 mA cm À 2 . The electrocatalyst also possesses superb stability at constant 10 mA cm À 2 current density for 50 h in all electrolytes. This work offers a synthesis protocol of a mixed-anion composite with the revelation about the importance of anion modulation towards electrode surface properties and HER performances.In recent years, different nanostructures and physical properties such as optical properties [9] and thermoelectricity [10] of transition-metal chalcogenides (TMCs) make them indispensable in various fields of research like energy conversion and storage, [11,12] dye-sensitized solar cells, [13] and photoelectrocatalysis. [14,15] Moreover, the inefficiency of energy-efficient electrodes in water electrolysis industry creates a potential market for highly efficient TMCs for electrocatalytic HER. [16,17] Recently, numerous TMCs, including CoS 2 , [18] CoSe x , [19,20] NiS 2 , [21] Ni 3 S 2 , [21] NiSe x , [22,23] SnSe 2 , [24] MoS 2 , [25] MoSe 2 , [26] WS 2 , [27] WSe 2 , [28] and ReSe 2 , [29] are studied for HER due to their low-cost and reasonable HER performances. However, individual metal sulfides or selenides as electrocatalysts exhibit nonideal electron transport and slow kinetics during HER because of their low electrical conductivities. More recently, Cu-based TMCs have garnered attention because of their abundant nature and low-cost. [30] For instance, Cu 2-x Se has an efficient HER activity in an acidic electrolyte, [31] but it is necessary to improve its HER performance in pH-universal electrolytes for commercialization. Recently published research works suggest that manipulation of the metal oxide surface is an useful direction for enhancing their HER performance because oxides such as NiO, [32] Co 3 O 4 , [33] Cu 2 O, [34] CeO 2 , [35] Mn 3 O 4 , [6] and TiO 2 [36] can participate in the reaction as water splitting promoters for HER. Although the use of Cu 2 O itself as a HER electrocatalyst is restrained due to its high overpotential and low current densities, the combination of Cu 2 Se with water dissociation promoters (Cu 2 O) by engineering the anion contents is expected to not only boost the HER kinetic but also optimize the free energy for hydrogen adsorption to achi...

Roles of Heterojunction and Cu Vacancies in the Au@Cu2–xSe for the Enhancement of Electrochemical Nitrogen Reduction Performance

“…The oxidation states and chemical composition of the surface elements in Au@Cu 2– x Se nanoparticles were investigated by using XPS. The Au 4f spectra (Figure b) can be deconvoluted into two peaks attributed to Au 4f 7/2 and Au 4f 5/2 , situated at 83.8 and 87.5 eV, respectively. , The prepared Au@Cu 2– x Se nanoparticles exhibited peaks at 931.7 and 951.6 eV corresponding to Cu 1+ and peaks at 933.5 and 953.3 eV related to Cu 2+ , along with satellite peaks at 942.9 and 961.9 eV in Cu 2p spectra (Cu 2p 3/2 and Cu 2p 1/2 ) (Figure c). ,, The Se 3d spectra in Figure d are deconvoluted into three peaks assigned to Se 3d 5/2 (53.8 eV), Se 3d 3/2 (54.9 eV), and SeO x (58.5 eV), respectively. − The SeO x peak emerged from the oxygen absorption on the surface of Au@Cu 2– x Se. The nonstoichiometric composition of the electrocatalyst surface, characterized by the presence of Cu 1+ and Cu 2+ , indicates the existence of Cu vacancies in Cu 2– x Se.…”

“…In addition to Au, the analysis of Cu species displayed characteristic peaks corresponding to the 2p 1/2 and 2p 3/2 spin− orbit spitting, representing Cu 1+ and Cu 2+ oxidation states. 41,43,44 The comparison of Cu 2p XPS spectra before and after NRR showed changes in the ratio of Cu 2+ to Cu 1+ state, indicating the influence of the electrochemical reaction on the oxidation of Cu. Similarly, the analysis of Se species exhibited peaks corresponding to the 3d 1/2 and 3d 3/2 spin− orbit spitting, representing the Se 0 and SeO x oxidation states of Se species.…”

“…41,42 The prepared Au@Cu 2−x Se nanoparticles exhibited peaks at 931.7 and 951.6 eV corresponding to Cu 1+ and peaks at 933.5 and 953.3 eV related to Cu 2+ , along with satellite peaks at 942.9 and 961.9 eV in Cu 2p spectra (Cu 2p 3/2 and Cu 2p 1/2 ) (Figure 2c). 41,43,44 The Se 3d spectra in Figure 2d are deconvoluted into three peaks assigned to Se 3d 5/2 (53.8 eV), Se 3d 3/2 (54.9 eV), and SeO x (58.5 eV), respectively. 45−47 The SeO x peak emerged from the oxygen absorption on the surface of Au@Cu 2−x Se.…”