Retracted: Earth‐Abundant Iron Diboride (FeB₂) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Abstract

energy conversion and storage. [1,2] Developing efficient electrocatalysts that can effectively enhance the sluggish kinetic processes are particularly important to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at low overpotentials. [3,4] Platinum group metals and noble metal oxides (e.g., IrO 2 , RuO 2 ) are considered as pioneering HER and OER catalysts, respectively. However, the large-scale applications are limited by the scarcity and high cost of these materials. [5,6] Recently, a great deal of effort and progress has been made toward the development of earth-abundant, highly efficient, and durable HER and OER catalysts, such as transition metal chalcogenides, [7][8][9] phosphides, [10][11][12] nitrides, [13][14][15] and carbides [16][17][18] (for HER), and transition metal oxide, [19][20][21] hydroxide/oxyhydroxide, [22][23][24] phosphate, [25][26][27] and carbon materials [28][29][30] (for OER). Due to the thermodynamic convenience and practical application in proton-exchange membrane or alkaline electrolyzers, these HER and OER catalysts generally exhibit high activity in strongly acidic and basic conditions, separately; thus pairing the two type catalysts in an integrated electrolyzer with high efficiency and stability for overall water splitting is difficult due to the mismatch of electrolyte pH. [31,32] There is Developing efficient, durable, and earth-abundant electrocatalysts for both hydrogen and oxygen evolution reactions is important for realizing largescale water splitting. The authors report that FeB 2 nanoparticles, prepared by a facile chemical reduction of Fe 2+ using LiBH 4 in an organic solvent, are a superb bifunctional electrocatalyst for overall water splitting. The FeB 2 electrode delivers a current density of 10 mA cm −2 at overpotentials of 61 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) in alkaline electrolyte with Tafel slopes of 87.5 and 52.4 mV dec −1 , respectively. The electrode can sustain the HER at an overpotential of 100 mV for 24 h and OER for 1000 cyclic voltammetry cycles with negligible degradation. Density function theory calculations demonstrate that the boron-rich surface possesses appropriate binding energy for chemisorption and desorption of hydrogen-containing intermediates, thus favoring the HER process. The excellent OER activity of FeB 2 is ascribed to the formation of a FeOOH/ FeB 2 heterojunction during water oxidation. An alkaline electrolyzer is constructed using two identical FeB 2 -NF electrodes as both anode and cathode, which can achieve a current density of 10 mA cm −2 at 1.57 V for overall water splitting with a faradaic efficiency of nearly 100%, rivalling the integrated state-of-the-art Pt/C and RuO 2 /C.

Designing Highly Efficient and Long‐Term Durable Electrocatalyst for Oxygen Evolution by Coupling B and P into Amorphous Porous NiFe‐Based Material

“…Ni 2p3/2 and Ni 2p1/2 core peaks and their satellite peaks are observed, with the core peaks being deconvoluted into two peaks at 855.65 and 857.23 eV and indexed to metallic Ni(OH) 2 and NiOOH, respectively. The B 1s spectrum can be deconvoluted into two peaks at 189.77 and 191.85 eV, and the former is ascribed to metallic borides while the latter can be assigned to oxidized borates species . The P 2p3/2 peaks at 132.70 eV are assigned to phosphates.…”

“…In the family of amorphous metallic materials, aiming at gaining a more efficient and stable catalyst, it would be promising to explore the synergistic effect of nonmetal elements on influencing the electron structure and OER behavior. B and P based metal compounds were both viewed as efficient OER electrocatalysts, which we believe the codoping of B and P in an amorphous metallic material will fulfill such situation and direct toward further enhancement of the catalytic and durable performance but lacks investigation.…”

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

“…Earth-abundant elementbased electrocatalysts, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] such as transition-metal oxides, carbides, sulfides, phosphides, and graphdiyne, are promising alternatives to precious electrocatalysts. RuO 2 /IrO 2 and Pt-based materials are currently considered as the state-ofthe-art electrocatalysts for OER in alkaline conditions and HER in acidic conditions, respectively.…”

Binary FeCo Oxyhydroxide Nanosheets as Highly Efficient Bifunctional Electrocatalysts for Overall Water Splitting

“…For sustained overall water splitting, it is desirable to couple HER and OER catalysts in the same electrolyte . Recently, much effort has been devoted to develop low‐cost and high‐efficiency bifunctional catalysts for the HER and OER using earth‐abundant elements . Grätzel and co‐workers reported a water electrolyzer constructed with a NiFe layered double hydroxide bifunctional catalyst, which achieved an overall water‐splitting current density of 10 mA cm −2 in 1 m NaOH solution at a cell voltage of ≈1.7 V ( iR uncorrected) with an overpotential of 470 mV from the equilibrium .…”

“…Grätzel and co‐workers reported a water electrolyzer constructed with a NiFe layered double hydroxide bifunctional catalyst, which achieved an overall water‐splitting current density of 10 mA cm −2 in 1 m NaOH solution at a cell voltage of ≈1.7 V ( iR uncorrected) with an overpotential of 470 mV from the equilibrium . Various bifunctional catalysts for water splitting based on transitional metal oxides, hydroxides, sulfides, phosphides, selenides, and borides have also been reported. Despite this progress, it is still necessary to develop a highly active and inexpensive bifunctional catalyst for water splitting in order to realize efficient hydrogen production.…”