Polarization Resistance‐Free Mn₃O₄‐Based Electrocatalysts for the Oxygen Reduction Reaction

Abstract

Transition metal oxides have been proposed as a possible replacement of platinum for the electrocatalytic oxygen reduction reaction (ORR). However, as a result of the low intrinsic conductivity, an application in electrocatalysis is challenging. In this work, we demonstrate that atomic layer deposition (ALD) is capable to overcome this problem by coating conductive carbon nanotubes substrates with a conformal Mn 3 O 4 layer of just few-nm in thickness. The deposition parameters have been optimized in terms of thickness and crystallite sizes to produce a material exhibiting catalytic efficiency close to the one of carbon-supported Pt particles and low polarization costs. The current densities recorded in linear sweep voltammetry prove that the Mn 3 O 4 coating leads to a substantial increase of the catalytic efficiency, compared to uncoated carbon nanotubes, and was also higher than other manganese-based catalysts reported so far. The sample prepared from only 50 ALD cycles (e. g. coating thickness of~2 nm) shows the best compromise between catalytic efficiency, with an onset potential at 0.867 V (vs. RHE), and good conductivity of the electrode materials minimizing polarization. Indeed, the Tafel plots exhibit a similar slope than Pt/C demonstrating that the Mn 3 O 4 /CNTs reduce oxygen in a one-step four electrons mechanism and with a similar kinetics as Pt-based electrocatalysts. Moreover, the current density keeps at 80 % even after 12 h at 0.58 V displaying a higher stability than Pt-based catalysts. These findings are attributed to the few nm-thick conformal and catalytic active coating obtained by atomic layer deposition, which also protects the underneath CNT substrate from corrosion.

Tuning the NiO Thin Film Morphology on Carbon Nanotubes by Atomic Layer Deposition for Enzyme‐Free Glucose Sensing

“…The SCCNTs were equally and conformally coated from the inner and the outer surfaces with NiO nanoparticles. The ALD film is made of small NiO nanoparticles after 25 ALD cycles, the particles grow up to 200 cycles showing a rough surface with an average particle size of 4 nm for S200 and then the layer became more dense due to the overlapping and increase in particles sizes, this is in the agreement with some previous reports from our group and some others ,. The average thickness calculated for samples coated with 25, 50, 100, 200, 400 and 700 ALD cycles is 0.8 nm, 1.7 nm, 4.0 nm, 6.5 nm, 14.0 nm and 21.8 nm, respectively.…”

“…Undoubtedly, ALD has been widely considered as a rising technology, which can execute the deposition of thin films over complex and high‐surface‐area substrates with uniformity, high conformity and precise size control at atomic level for the fabrication and surface modification of nanocomposites ,. Although, ALD technology has been broadly used in electrocatalysis and electrochemical energy storage, it has been barely used in electrochemical sensors ,. Promising electrochemical performances conferred by few ALD synthesized NiO‐based nanocomposites revealed the significance to extend the application for tuneable synthesis of nanocomposites with controlled particle size and thickness of the functional films in electrochemical detection ,.…”

Co/CoP Nanoparticles Encapsulated Within N, P-Doped Carbon Nanotubes on Nanoporous Metal-Organic Framework Nanosheets for Oxygen Reduction and Oxygen Evolution Reactions

“…The development of modern society depends on energy supply to a large extent, but with environmental problems induced by the burning of fossil fuels and the aggravation of energy shortage, it is necessary to find new conversion systems or renewable energy [1][2][3][4]. Fuel cells and metal-air batteries are considered to be promising energy systems; however, their poor energy conversion efficiency and short life span are the main bottlenecks that limit their widespread use [5][6][7][8][9]. These deficiencies are primarily on account of the inherent sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) [10][11][12][13].…”

Investigations of Carbon Nitride-Supported Mn3O4 Oxide Nanoparticles for ORR

“…Calcination in air was deemed to be important for improving the ORR active site density, whilst incorporation of multi-walled carbon nanotubes (MWCNTs) lead to an overall improvement of stability and activity, due to the higher conductivity. Various crystalline phases of Mn oxide, along with an amorphous phase, were shown to have strong OER and ORR activity under alkaline conditions, with activity varying significantly with phase [22,23].…”

“…Under alkaline conditions (pH 11.35 to 13.30) they observed Mn in an average oxidation state of 3.68+, showing a mixture of Mn(III) and Mn(IV) species to be present. N-doping of water splitting catalysts has been shown to be beneficial on a number of occasions [23,24]. The improvements of catalysts with the addition of nitrogen seems to be dependent on the nitrogen-metal interaction, which has been shown to be very significant for a range of metals, including cobalt, tungsten, and manganese.…”