Borohydride Oxidation Reaction Research Articles

Pt-decorated binary transition metal oxides (MnO-NiO, MnO-TiO2) for enhanced electrocatalysis of oxygen reduction and borohydride oxidation

Integrating transition metal oxides with precious metals is a strategic approach to designing cost-effective electrocatalysts with enhanced stability. Herein, platinum (Pt) nanoparticles (NPs) were prepared by microwave irradiation and anchored onto MnO and two binary metal oxides, MnO-NiO and MnO-TiO2, obtained by solid-state dispersion. Voltammetric and electrochemical impedance spectroscopy techniques evaluated their performance for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) in alkaline media. Tafel slope and the number of exchanged electrons, n, were determined to compare the three electrocatalysts’ performance for fuel cell applications. Pt/MnO-NiO revealed a Tafel slope of 177 mV dec–1 for ORR and an n value of ca. 4 and 3 e- for ORR and BOR, respectively. These findings demonstrate that Pt NPs supported on binary metal oxide supports, particularly Pt/MnO-NiO, are promising electrocatalysts for ORR and BOR in alkaline media, thus recommending their use in direct borohydride fuel cells.

Engineering Partially Oxidized Gold via Oleylamine Modifier as a High-Performance Anode Catalyst in a Direct Borohydride Fuel Cell.

Direct borohydride fuel cell (DBFC) is considered a promising energy storage device due to its high theoretical cell voltage and energy density. For DBFC, an Au catalyst has been used as an anode for achieving an ideal eight-electron reaction. However, the poor activity of the Au catalyst for borohydride oxidation reaction (BOR) limits its large-scale application because of the weak BH4- adsorption. We found, by density functional theory calculations, that the adsorption of BH4- on the oxidized Au surface is stronger than that on the metallic Au surface, which can promote the process of the oxidation of BH4- to *BH3 during the BOR. Here, we reported an oleylamine-modified partially oxidized Au supported on carbon powder (AuC-OLA) with a stable oxidation state. The obtained catalyst delivered a high peak power density of 143 mW/cm2, which is 2 times higher than that of a commercial 40% AuC (Pretemek). The in situ Fourier transform infrared studies showed that the activity of AuC-OLA for BOR is ascribed to the enhanced adsorption for BH4- on the partially oxidized Au surface. These findings will promote the reasonable design of efficient Au electrocatalysts for DBFCs.

Boosting borohydride oxidation kinetics by manipulating hydrogen evolution and oxidation through octahedral Pt–Ni/C for high-performance direct borohydride fuel cells

Direct borohydride fuel cells (DBFCs) outperform the other direct liquid fuel cells by a higher open circuit voltage and energy density. However, their benign performance and efficiency are highly dependent on high-performance anode catalysts. This study delves into the enhancement of borohydride oxidation reaction (BOR) kinetics through an octahedral Pt–Ni/C catalyst. The Pt(111) facets of the catalyst exhibit a combination of abundant active sites exposed for BOR and the inherent ability to suppress hydrolysis reaction. Furthermore, the synergistic incorporation of Ni modifies the electronic structure of Pt, resulting in enhanced OH− adsorption and hydrogen oxidation reaction (HOR) activity. This multifaceted approach not only mitigates hydrogen accumulation but also boosts the overall BOR efficiency. The elaborate electrochemical measurements along with comprehensive characterizations elucidate the superior catalytic activity and stability of Pt–Ni/C over commercial Pt/C catalysts. Specifically, DBFCs employing the Pt–Ni/C catalyst manifest considerably higher open circuit voltage (1.05 V), peak power density (1.82 W cm−2) and fuel efficiency (63.96 %) than those of DBFCs employing Pt/C catalyst. Through these efforts, we provide significant insight into the design of high-performance anode catalyst for DBFCs.

Performance enhancement for direct borohydride fuel cells through ternary Ru–Co–B oxide catalyst

Dielectric barrier discharge (DBD) plasma is used to prepare ternary heterostructured Ru–Co–B oxide catalyst with considerable RuO2/CoO/B20H26O interface and oxygen vacancy (Ov) for enhanced borohydride oxidation reaction. the Ru–Co–B catalyst displayed remarkable electrocatalytic activity and long-term stability Due to the difference in energy band structure at the interface where the charge distribution is not homogeneous, the heterogeneous structure will spontaneously generate a built-in electric field which prompts the interfacial charge transfer. The production of Ov increases its active site and promotes its catalytic activity. While it is used in membrane-less direct borohydride fuel cells (DBFCs), it showed a peak power density of 206 mW cm−2 at room temperature and a remarkable stability of 270 h at a constant current of 20 mA that is superior to commercial Pt/C.

Two birds with one stone: valence and substrate microenvironment engineering of Co-based catalysts for high-performance borohydride oxidation reaction

Direct borohydride fuel cells (DBFCs) urgently need a deep understanding of the electronic structure–activity relationship of the transition metal-based electrode-catalyzed borohydride oxidation reaction (BOR) and an effective strategy to mitigate bubble effect. In this work, phosphorus (P) and oxygen (O) heteroatoms are utilized to regulate the low-valent Co content with high activity towards BOR in the catalytic center, while concurrently modifying the electronic structure of C to construct a microenvironment with strong adsorption for Hatom. The interfacial synergistic effects between the catalytic center and the microenvironment optimize the Hatom reaction pathway to mitigate the bubble effect and enhance fuel utilization. As a result, a record-high peak power density of 806 mW cm−2 is achieved with a CoP/O-C anode in the DBFCs. Macro high-speed camera reveals that the bubble density on the electrode surface is effectively mitigated. This work provides insight and feasible engineering strategies for studying valence-activity and microenvironment-selectivity relationships.

Polypyrrole regulates Active Sites in Co-based Catalyst in Direct Borohydride Fuel Cells.

Direct borohydride fuel cells (DBFCs) convert borohydride (NaBH4) chemical energy into clean electricity. However, catalytic active site deactivation in NaBH4 solution limits their performance and stability. We propose a strategy to regulate active sites in Co-based catalysts using polypyrrole modification (Co-PX catalyst) to enhance electrochemical borohydride oxidation reaction (eBOR). As an anode catalyst, the synthesized Co-PX catalyst exhibits excellent eBOR performance in DBFCs, with current density of 280 mA ⋅ cm-2 and power density of 151 mW ⋅ cm-2, nearly twice that of the unmodified catalyst. The Co-PX catalyst shows no degradation after 120-hour operation, unlike the rapidly degrading control. In-situ electrochemical attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIRS) and density functional theory (DFT) suggest that polypyrrole-modified carbon support regulate the charge distribution, increasing oxidation state and optimizing adsorption/desorption of intermediates. A possible reaction pathway is proposed. This work presents a promising strategy for efficient polymer-modulated catalysts in advanced DBFCs.

AuAg/rGO elektrode za reakciju oksidacije borhidrida

Gold and silver nanoparticles in different atomic ratios deposited on reduced graphene oxide (AuAg/rGO-1, AuAg/rGO-2, and AuAg/rGO-3) were tested for the borohydride oxidation reaction in an alkaline medium. The morphology, structure, and composition of AuAg/rGO electrodes were investigated by transmission electron microscopy (TEM) and scanning electron microscopy with integrated energy dispersive spectroscopy (SEM-EDS). The TEM analysis showed that the most of gold and silver particles (more than 80%) are up to 9 nm in size, while slightly larger particles represent less than 5%. SEM-EDS showed a similar morphology, and the composition of three AuAg/rGO electrodes was determined. AuAg/rGO-1 and AuAg/rGO-2 electrodes showed similar, while AuAg/rGO-3 electrodes demonstrated slightly lower electrocatalytic activity for borohydride oxidation. The studied electrodes were observed to be active for the borohydride hydrolysis as well, which is expected based on literature data. AuAg/rGO certainly represent potential anode materials for application in direct borohydride fuel cells.

Drop-cast gold nanoparticles are not always electrocatalytically active for the borohydride oxidation reaction

A collection of single Au nanoparticles (NPs) and NP clusters were individually tested for the borohydride oxidation reaction. Significant variation in the activity could not be attributed to NP size, and ∼67% of NP locations displayed no activity.

Au-Based MOFs as Anodic Electrocatalysts for Direct Borohydride Fuel Cells

Researchers are exploring direct liquid fuel cells (DLFCs) as alternatives to proton-exchange membrane fuel cells because of their higher energy density and ease of storing and transporting the fuel. Direct borohydride fuel cells (DBFCs) are of particular interest as they offer a sustainable energy source with their high-power density output and the use of a highly alkaline NaBH4 medium [1]. Ensuring efficient and cost-effective catalysts for DBFCs is crucial for their commercial viability. Metal-organic frameworks (MOFs) have demonstrated significant potential as anodic electrocatalysts for BOR in DBFCs [2]. However, research should explore various modifications to MOFs, such as the incorporation of alternative metal ions or functional groups, to improve their catalytic efficiency and reduce cost. This study evaluated the performance of newly developed MOF-based electrocatalysts for DBFCs. Specifically, six MOF-based materials were synthesized and analyzed for their ability to facilitate borohydride oxidation (BOR) using cyclic voltammetry and chronoamperometry in alkaline media. MIL-101_Au@NH2 and MOF-808_Au@NH2 were found to be highly effective for BOR. The kinetic parameters for BOR with MOF-based electrocatalysts, including activation energy, reaction order, exchanged electrons, and anodic charge transfer coefficient, were determined. The activation energy for BOR was found to be 13.6 kJ mol−1 and 15.3 kJ mol−1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. The number of transferred electrons, n, was found to be 7.0 and 3.1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. This study demonstrates that MOF-based electrocatalysts can enhance DBFCs' performance, while offering insight into the potential usage of MOFs in other fuel cell technologies.[1] B. Šljukić, D.M.F. Santos, "Direct borohydride fuel cells", in: "Direct Liquid Fuel Cells: Fundamentals, Advances, and Future", 1st ed., R.G. Akay, A.B. Yurtcan (eds.), Academic Press, USA, 203-232 (2021)[2] G. Backovic, B. Šljukić, G.S. Kanberoglu, M. Yurderi, A. Bulut, M. Zahmakiran, D.M.F. Santos, Ruthenium (0) nanoparticles stabilized by the metal-organic framework as an efficient electrocatalyst for borohydride oxidation reaction, International Journal of Hydrogen Energy, 45, 27056-27066 (2020).

From nickel waste solution to hydrogen storage alloys – An excellent example of circular economy implementation

In light of the need to protect the environment from hazardous heavy metals, waste management is becoming not just a proposal but a necessity for the reduction of wastewater toxicity and, additionally, a value-added substitute for processes of extracting raw materials from primary sources. This article demonstrates the feasibility of using critical and hazardous element as Ni(II) from industrial nickel waste solutions to produce hydrogen storage alloys (HSA), perfectly fulfilling the circular economy assumptions. The hydrometallurgical process proposed for the preparation of the Ni-containing electrolyte (NiE) from the waste solution included the following stages: diffusion dialysis, Cr(III) and Al(III) hydroxide precipitation, extraction to separate Co(II) from Ni(II), and the organic phase regeneration by Co(II) stripping with dialysate. The raffinate after extraction performed as NiE (∼10–15 g/dm3 Ni(II), 0.1 g/dm3 Co(II)) for the preparation of HSA. However, to improve the quality of Ni deposit on NiCo foam or steel plates, NiE should be modified with an ammonia solution (to pH ∼ 12). A better voltammetric characteristic of the modified electrodes (25–30 percentage points higher peaks resulting from NaBH4 electrooxidation), compared to those unmodified was reported. It was proven that the electroactive materials obtained showed high catalytic performance for the borohydride oxidation reaction.

Combining silver, polyaniline and polyvinylpyrrolidone for efficient electrocatalysis of borohydride oxidation reaction

The catalytic activity of five silver-polyaniline-polyvinylpyrrolidone (Ag@PANI@PVP1–5) nanocomposites for borohydride oxidation reaction (BOR) was thoroughly examined. The nanocomposites were synthesized by an in situ chemical oxidative polymerization of aniline monomer by Ag+ ions in the presence of accelerator – PVP and physicochemical properties were determined prior their use in electrocatalysis. Ag@PANI@PVP3 with 35.4 wt% Ag delivered the highest current density and specific current density during BOR. Evaluation of the order of reaction < 1 suggested indirect BOR mechanism. Furthermore, Ag@PANI@PVP3 also delivered the highest current density and stable performance during chronoamperometric study of BOR. Its apparent activation energy of 15 kJ mol−1 was found to be the lowest among the studied materials accounting for the high current densities.

From PET Bottles Waste to N-Doped Graphene as Sustainable Electrocatalyst Support for Direct Liquid Fuel Cells

Direct liquid fuel cells represent one of the most rapidly emerging energy conversion devices. The main challenge in developing fuel cell devices is finding low-cost and highly active catalysts. In this work, PET bottle waste was transformed into nitrogen-doped graphene (NG) as valuable catalyst support. NG was prepared by a one-pot thermal decomposition process of mineral water waste bottles with urea at 800 °C. Then, NG/Pt electrocatalysts with Pt loadings as low as 0.9 wt.% and 1.8 wt.% were prepared via a simple reduction method in aqueous solution at room temperature. The physical and electrochemical properties of the NG/Pt electrocatalysts are characterized and evaluated for application in direct borohydride peroxide fuel cells (DBPFCs). The results show that NG/Pt catalysts display catalytic activity for borohydride oxidation reaction, particularly the NG/Pt_1, with a number of exchanged electrons of 2.7. Using NG/Pt composite in fuel cells is anticipated to lower prices and boost the usage of electrochemical energy devices. A DBPFC fuel cell using NG/Pt_1 catalyst (1.8 wt.% Pt) in the anode achieved a power density of 75 mW cm−2 at 45 °C. The exceptional performance and economic viability become even more evident when expressed as mass-specific power density, reaching a value as high as 15.8 W mgPt−1.

Lattice strain controlled Ni@NiCu efficient anode catalysts for direct borohydride fuel cells.

We successfully fabricated a novel tensile lattice strained Ni@NiCu catalyst with a popcorn-like morphology, which is composed of a crystalline Ni core and a NiCu alloy shell. It exhibits outstanding catalytic activity, selectivity, and stability towards borohydride electrooxidation. Moreover, a direct borohydride fuel cell (DBFC) with a Ni@NiCu anode can deliver a power density of 433 mW cm-2 and an open circuit voltage of 1.94 V, much better than the performances of DBFCs employing other anode catalysts reported in the literature. This could be attributed to the fact that the tensile lattice strain generated by the introduction of Cu leads to a rise in the d-band center of the Ni metal and promotes the final B-H decoupling, which is the rate-determining step in the borohydride oxidation reaction, thus improving remarkably the catalytic performances of Ni@NiCu.

Succulent-plant-like Ni-Co alloy efficient catalysts for direct borohydride fuel cells.

A Ni-Co alloy catalyst with a unique succulent-plant-like morphology is prepared by a simple electrodeposition method, while the effects of deposition conditions on its performance are also investigated systematically. The research results show that the Ni0.889-Co0.111 catalyst exhibits excellent activity, selectivity, and stability to the borohydride oxidation reaction. Moreover, when Ni0.889-Co0.111 is assembled as the anode catalyst, the direct borohydride fuel cell delivers a peak power density of 490 mW cm-2 and an open-circuit voltage of 1.87 V at 343 K and can run stably for dozens of hours. The significant improvement in Ni-Co catalyst performance can be attributed to its unique succulent-plant-like morphology and the introduction of an appropriate amount of Co.

Electrodeposited NiCu nanoparticles for the borohydride oxidation reaction: Effect of Cu on the activity and stability of Ni upon surface oxidation

Development cost-effective and stable electrocatalysts for the borohydride oxidation reaction (BOR) is mandatory for the deployment of the direct borohydride fuel cells (DBFC). Ni electrocatalysts have recently been shown to outperform noble-metal (Pt, Pd, Au) catalysts at low BOR overpotentials, but their activity largely depends on the state of the Ni surface with metallic Ni demonstrating the highest activity. Here, bimetallic NiCu nanoparticles of different compositions were prepared, which demonstrate high BOR activity comparable to Ni nanoparticles in the metallic state of their surface and allow to overcome in considerable extent the negative issues related to inevitable surface passivation.

High-performance metal (Au,Cu)–polypyrrole nanocomposites for electrochemical borohydride oxidation in fuel cell applications

Gold polypyrrole (AuPPy) and copper polypyrrole (CuPPy) nanocomposites were prepared by a simple one-step in situ oxidative polymerization of pyrrole monomer by Au3+ and Cu2+ ions. Owing to their characteristic physicochemical properties confirmed by optical and structural characterization methods, the behavior of these materials as electrocatalysts for borohydride oxidation reaction (BOR) was considered. BOR apparent activation energy was found to be 16 and 22 kJ mol−1 for AuPPy and CuPPy electrocatalyst, respectively. The stability of the two electrocatalysts was assessed by chronoamperometry. Moreover, fuel cell tests were carried out with AuPPy and CuPPy as anode electrocatalyst of a direct borohydride-peroxide fuel cell (DBPFC). Open circuit voltage (OCV) of 1.30 V was obtained with both AuPPy and CuPPy, with the OCV increasing to 1.45 V upon adding a small amount of carbon (AuPPy-C). The peak power density of a DBPFC with BOR at AuPPy-C anode and hydrogen peroxide reduction reaction at Pt cathode was found to be ca. 162 mW cm−2 at 65 °C.

Single‐Entity Electrochemical Detection of As‐Prepared Metallic and Dielectric Nanoparticle Stochastic Impacts in a Phosphonium Ionic Liquid

AbstractNanoparticles (NPs) are of considerable interest, owing to their enhanced catalytic activity and optical properties. Ionic liquids (ILs) are employed as a medium to prepare small (&lt;20 nm in diameter) and relatively low dispersity (typically, ±1–2 nm) NPs. While ensemble techniques (e. g., UV/Vis) can provide a great deal of information, increasingly, single‐entity electrochemistry (SEE) has been used to provide physical insight into individual NP catalysis and dynamics. Herein, Pt NP impact current spikes for particles prepared in the IL phase and based on electrocatalytic amplification (ECA) of the borohydride oxidation reaction (BOR) were recorded during i‐t measurements. Additionally, direct oxidative LiBH4 nanocrystal (NC) impact signals were observed herein for the first time. By quantifying the charge transferred during the stochastic collision events, the radius of the NCs (rNC) was calculated (∼5.5 nm) and compares favorably with TEM images. Critically, small additions (1 % v/v) of a molecular, polar organic solvent (tetrahydrofuran, THF) disrupt the ILs supramolecular fluidic nature, which enhances NC impact frequency and the aggregation of Pt NPs.

Carbon Coated and Nitrogen Doped Hierarchical NiMo-Based Electrocatalysts with High Activity and Durability for Efficient Borohydride Oxidation

Sodium borohydride is a promising candidate as hydrogen storage material. The direct borohydride fuel cell (DBFC) as an energy conversation device has attracted intensive attention owing to the low theoretical potential of borohydride oxidation reaction (BOR, -1.24 V vs SHE) on the anode. In this paper, the hierarchical sea urchin-like NiMoN@NC coated by thin carbon layer with optimal BH4- adsorption characteristic was synthesized as a superior electrocatalyst toward BOR. In 1 M NaOH-0.05 M NaBH4, the BOR working potentials are only -55 and 44 mV at the current densities of 10 and 200 mA cm-2 on NiMoN@NC, respectively. Furthermore, the membrane-free DBFC using NiMoN@NC as anodic electrocatalyst shows a maximum power density of 67 mW cm-2 at room temperature with appreciative stability. This well-designed carbon coated and nitrogen doped transition-metal material with hierarchical nano/microstructure as a highly efficient electrocatalyst shows promising potential and bright prospects in electrocatalysis research and practical application for energy conversion systems of DBFC.

Direct borohydride fuel cells: A selected review of their reaction mechanisms, electrocatalysts, and influence of operating parameters on their performance

Direct borohydride fuel cells (DBFC) oxidize an easily-stored energy-dense borohydride fuel (sodium borohydride: NaBH 4 ), that in theory reacts ca . 400 mV below H 2 and produces 8 electrons per BH 4 - anion. However, the borohydride oxidation reaction (BOR) does not fully meet these promises in practice: the electrocatalyst nature, structure and state-of-surface, and the operating conditions (pH, BH 4 - concentration, temperature, fluxes) noticeably influence the BOR kinetics and mechanism. Nickel and platinum-based catalysts both have assets for the BOR. DBFCs can only yield decent performance if their separator combines high ion-conductivity and efficient separation of the reactants; cation-exchange membranes, anion-exchange membranes, bipolar membranes and porous separators all have their own advantages and drawbacks. Besides the anode, the choice of separator must consider the DBFC cathode reaction, where oxygen (usually from air) or hydrogen peroxide are reduced, provided adapted catalysts are used. All these aspects drive the DBFC performance and stability/durability. • The BOR kinetics/mechanism strongly depends on the catalyst and operating parameters. • Metallic nickel is highly efficient at low potential values but leads to high H 2 escape. • Platinum leads to fast kinetics of the H 2 production from BH 4 - and fast H 2 oxidation. • Depending on the membrane/separator, DBFC must employ BH 4 - tolerant cathodes. • The morphology of the electrode, diffusion medium and bipolar plate channels impact mass-transport hence DBFC performance.

Selective Borohydride Oxidation Reaction on Nickel Catalyst with Anion and Cation Exchange Ionomer for High‐Performance Direct Borohydride Fuel Cells (Adv. Energy Mater. 16/2022)

Borohyride Fuel Cells In article number 2103539, Andreas Züttel and co-workers develop a facile synthesis method for a nickel catalyst and ionomer composite for replacing palladium catalysts in direct borohydride fuel cells (DBFCs). The DBFC operates with a liquid fuel (anode: sodium borohydride solution, cathode: hydrogen peroxide solution) to generate electricity.