Hydrothermal Synthesis of Monolithic Co₃Se₄ Nanowire Electrodes for Oxygen Evolution and Overall Water Splitting with High Efficiency and Extraordinary Catalytic Stability

Abstract

using electrocatalysts, the OER will take place at a high overpotential leading to significant losses of the overall efficiency of water splitting. Although RuO 2 and IrO 2 are highly efficient catalysts for the OER, [1b] the exorbitant price and scarcity of Ru and Ir severely restrict their widespread use in electrolyzers.Remarkable progress has been made in developing efficient nonprecious OER electrocatalysts, such as perovskite oxides, [3] transition metal (TM) oxides, [4] (oxy)hydroxides, [5] phosphates, [6] phosphides, [7] nitrides, [8] chalcogenides, [9] and metal-free carbon nanostructures. [10] Recently, cobalt selenide with different polymorphs has attracted considerable attention for use as efficient catalysts to expedite the OER in basic solution [9a-f ] or the HER in acidic solution, [11] most of which were prepared by a two-step method involving either the synthesis of Co-containing precursors followed by a selenization process, [11a-f ] or the synthesis of selenide precursors followed by a cation-exchange process. [9f ] Since the high OER activity expected for pure cobalt selenide remains out of reach, strategies that can enhance the OER activity of cobalt selenide have been explored. For example, composites of CoSe 2 with graphene [9d] or metal oxides [9a,e] were reported, and exhibited OER activity substantially higher than that of pure CoSe 2 . The enhanced OER activity is believed to result from the synergistic interaction between cobalt selenide and graphene/ metal oxides. [9a,d,e] Besides, ultrathin CoSe 2 nanosheets (NSs) and atomic layers were synthesized by delaminating lamellar hybrid CoSe 2 -DETA (DETA = diethylenetriamine) intermediates, with the aim of exposing more low-coordinated catalytically active sites and achieving better structural stability. [9b,c] These NSs and single-unit-cell atomic layers have accomplished substantially improved OER activity compared to both bulk CoSe 2 and CoSe 2 -DETA intermediates, requiring only a low overpotential (η) of 320 mV at 10 mA cm −2 in basic medium and showing a small Tafel slope of 44 mV decade −1 (dec −1 ). [9b] While CoSe 2 is still the most commonly studied polymorph of cobalt selenide, [9a−f,11] nonstoichiometric cobalt selenide (e.g., Co 0.85 Se) has drawn great attention very recently Cobalt selenide has been proposed to be an effective low-cost electrocatalyst toward the oxygen evolution reaction (OER) due to its well-suited electronic configuration. However, pure cobalt selenide has by far still exhibited catalytic activity far below what is expected. Herein, this paper for the first time reports the synthesis of new monoclinic Co 3 Se 4 thin nanowires on cobalt foam (CF) via a facile one-pot hydrothermal process using selenourea. When used to catalyze the OER in basic solution, the conditioned monolithic selfsupported Co 3 Se 4 /CF electrode shows an exceptionally high catalytic current of 397 mA cm −2 at a low overpotential (η) of 320 mV, a small Tafel slope of 44 mV dec −1 , a turnover frequency of 6.44 × 10 −2 ...

Multifunctional Single‐Crystallized Carbonate Hydroxides as Highly Efficient Electrocatalyst for Full Water splitting

“…[1][2][3][4] However, the development of practical full water splitting (FWS) applications encountered very serious challenges: the sluggish kinetics of OER and HER. [21,22] Inspired by above considerations, we here report the fabrication of Fe-doped Co carbonate hydroxide nanosheets array on 3D conductive Ni foam (FCCH/NF) as a monolithic OER-HER bifunctional electrocatalyst for FWS. Additionally, the direct growth of catalyst grown on 3D conductive substrates has been considered to be an effective way for exposing more active sites, facilitating mass transport, and thus leading to more efficient use of active sites and increasing the electrical conductivity.…”

A New Class of Zn1‐xFex–Oxyselenide and Zn1‐xFex–LDH Nanostructured Material with Remarkable Bifunctional Oxygen and Hydrogen Evolution Electrocatalytic Activities for Overall Water Splitting

“…For electrocatalysis, “d” electrons present in transition metals participate in bonding with adsorbates; thus the introduction of low electronegativity “Se” into the Zn 1‐ x Fe x –LDH can effectively modify the “d” orbital electronic structure and enhances the electrocatalytic activities . Besides, in order to find the electrochemical active surface area (ECSA) of Zn 1‐ x Fe x –LDH and Zn 1‐ x Fe x –oxyselenide, the previously established ECSA = C dl / C s equation was used, where C dl is electrochemical double‐layer capacitance and C s is specific capacitance of a flat smooth surface of the electrode material, which is presumed to be 40 mF cm −2 according to previous reports . Non‐Faradaic region (1.02–1.22 V vs RHE) cyclic voltammograms (Figure S3a,b, Supporting Information) at scan rates of 50–150 mV s −1 were used for C dl calculation, which was estimated by plotting the difference of the anodic and cathodic current densities (Δ j = j a − j c ) at 1.1 V versus scan rate (Figure S3c,d, Supporting Information).…”

“…During OER and HER stability studies, the electrode materials are expected to undergo structural/morphological changes and then affect the electrocatalytic performance. Very recent studies have demonstrated that under OER operational conditions non‐oxide‐based transition metal (TM) catalysts undergoes an in situ electrochemical transformation and form TM‐based hydroxide/(oxy)hydroxide, which is found to be the true catalytically active species for the OER. Moreover, it has been shown that in most cases the in situ transformed TM hydroxide/(oxy) hydroxide exhibits better OER performance than the pristine TM hydroxide/(oxy)hydroxide obtained by direct synthesis .…”

Nickel–Cobalt Diselenide Nanosheets Supported on Copper Nanowire Arrays for Synergistic Electrocatalytic Oxygen Evolution

“…[36] In integrated electrode, rational design of catalysts and current collector should be seriously addressed, including increasing effective active sites of the catalyst and promoting electron transport from active catalyst to external circuit via current collector. [38,39] Meanwhile, the core/shell nanowire array structure is beneficial to promote gas release and electrolyte permeation, and realize full contact between electrolyte and catalyst. 3D hierarchical architecture with core/shell nanowire array surface morphology is a kind of high aspect ratio structure, and can significantly accelerate electron transport and increase effective catalytic active sites of catalyst.…”