Synthesis of a Highly Efficient Oxygen‐Evolution Electrocatalyst by Incorporation of Iron into Nanoscale Cobalt Borides

Abstract

High-performance catalysts for the oxygen-evolution reaction in water electrolysis are usually based on expensive and rare elements. Herein, mixed-metal borides are shown to be competitive with established electrocatalysts like noble metal oxides and other transition-metal(oxide)-based catalysts. Iron incorporation into nanoscale dicobalt boride results in excellent activity and stability in alkaline solutions. (Co Fe ) B shows an overpotential of η=0.33 V (1.56 V vs. RHE) at 10 mA cm in 1 m KOH with a very low onset potential of ≈1.5 V vs. RHE, comparable to the performance of IrO and RuO . XPS shows that the original catalyst is modified under the reaction conditions and indicates that CoOOH and Co(OH) are formed as active surface species, whereas the Fe remains in the catalyst, contributing to an improved catalyst performance. The nanoscale borides are obtained by a one-step solution synthesis, calcined, and characterized by XRD, energy-dispersive X-ray spectroscopy, and SEM. Single crystals of (Co Fe ) B grown under chemical transport conditions were used for an unambiguous specification of the nanostructured particles by relating the cobalt/iron ratio to the lattice parameters.

The Role of Non‐Metallic and Metalloid Elements on the Electrocatalytic Activity of Cobalt and Nickel Catalysts for the Oxygen Evolution Reaction

“…Since these studies, no reports on electrocatalysis of the OER by metal borides can be found up until 2016 when activation of amorphous cobalt boride for electrocatalytic OER was reported . Several reports on the use of metal borides and metal borates as electrocatalysts for the OER have since been published, including mixed metal borides, and metal borides supported on carbon materials, and metallic substrates . Other strategies for utilizing the beneficial effects of boron incorporation into cobalt and nickel include surface boronization of metal or metal oxides surfaces .…”

Tailoring of Metal Boride Morphology via Anion for Efficient Water Oxidation

“…The high-resolution XPS (HRXPS) spectrum of C 1s (Figure 2b) exhibits four peaks at 284.5, 285.2, 286.2, and 288.9 eV BE for CC (sp 2 ), CC (sp 3 ), CO, and C  O, typical of C 1s spectrum of graphitic carbon which is from CNT. [13] The former reflects the interaction of B and metal, while the latter is from oxidized B due to exposure to air. [13] The former reflects the interaction of B and metal, while the latter is from oxidized B due to exposure to air.…”

“…[4b,11] This agrees with the literature that metal borides undergo severe oxidation, and hence, the presence of metal oxides and hydroxides is unavoidable. [13] The OER performance of the as-prepared materials was tested using a standard three-electrode setup in 1.0 m KOH. [13] The OER performance of the as-prepared materials was tested using a standard three-electrode setup in 1.0 m KOH.…”

“…Figure 2c shows the HRXPS spectrum of B 1s, which can be deconvoluted into two sub-peaks located at 187.9 and 191.9 eV BE, ascribed to the BM and BO bond mainly due to B 2 O 3 and other boron-oxo species, respectively. [13] The former reflects the interaction of B and metal, while the latter is from oxidized B due to exposure to air. [14] The presence of B interacting with metals which are catalytic active sites implies electron transfer to the d bands of the transition metal from B as revealed by a positive shift in BE compared to elemental B (187.2 eV), [10a] and as consequence, metal atoms are electron-rich which makes them highly active for catalytic reactions.…”

“…[11] The O 1s XPS spectrum in Figure 2f shows no peak at BE of lattice O, instead, the peaks at 531.6 and 533.4 eV ascribed to surface O and adsorbed O, [16] respectively, were observed emphasizing the predominance of oxidized species on the surface. [13] The OER performance of the as-prepared materials was tested using a standard three-electrode setup in 1.0 m KOH. All potentials reported are referenced to the reversible hydrogen electrode (RHE).…”