Category Archives: ChemElectroChem

Stability of Bipolar Plate Materials for Proton‐Exchange Membrane Water Electrolyzers: Dissolution of Titanium and Stainless Steel in DI Water and Highly Diluted Acid

Posted on 20 September 2023 by

We studied the stability of bipolar plate materials on-line. To mimic application-near conditions, we measured in deionized water and 0.5 mM H₂SO₄. For titanium, the dissolution is negligible, whereas for stainless steel 316L notable dissolution is detected. Yet, it remained below the reported poisoning limit for Nafion-based proton exchange membranes.

Abstract

The widespread use of proton exchange membrane water electrolyzers (PEMWE) is hindered by their high cost, of which a colossal factor is caused by the bipolar plates (BPP). In this paper, we investigate the stability of two BPP materials on-line with an optimized scanning flow cell setup coupled to an inductively coupled plasma mass spectrometer (SFC-ICP-MS), as well as scanning electron microscopy (SEM). The stability of currently used titanium and a cheaper alternative, stainless steel (SS) 316L, were characterized in deionized (DI) water and 0.5 mM H₂SO₄ to mimic the conditions at the BPP under operation. We show that the dissolution of Ti is negligible, whereas SS 316L degrades notably. Here, besides pH, the applied potentials play a crucial role. Nonetheless, even for the highest measured dissolution rate of SS 316L, the contamination in a full cell is estimated to remain below 1 ppm. This work illustrates the capabilities of on-line high-throughput stability tests for BPP materials and could therefore contribute towards optimization of cost-effective PEMWE.

Electrocatalytic Reduction of (Hetero)Aryl Halides in a Proton‐Exchange Membrane Reactor and its Application for Deuteration

Posted on 12 September 2023 by

We developed an electrocatalytic reduction of (hetero)aryl halides to substitute the halogeno groups to protons using a proton exchange membrane (PEM) reactor. Taking advantage of this transformation, deuterodehalogenation of (hetero)aryl bromides, which forms mono-deuterated (hetero)aryls, was demonstrated using heavy water as a deuterium source. The deuteration reaction was able to be optimized by Bayesian.

Abstract

We developed an electrocatalytic reduction of (hetero)aryl halides under mild conditions using a proton exchange membrane (PEM) reactor. This approach allows substituting the halogeno groups on the aryl rings to protons by water and electron. Taking advantage of this transformation, deuterodehalogenation of (hetero)aryl halides, which forms mono-deuterated (hetero)aryls, was demonstrated using heavy water as a deuterium source. The current efficiency and deuterium ratio could be increased by the conditions optimized by machine-learning method, Bayesian optimization.

Synthesis and Characterization of a Highly Electroactive Composite Based on Au Nanoparticles Supported on Nanoporous Activated Carbon for Electrocatalysis

Posted on 8 September 2023 by

Electrocatalysis: Gold nanoparticles with diameter between 5 and 20 nm evenly distributed onto porous activated carbon (Norit) were obtained using a facile “one-pot” chemical synthesis technique with very high metal utilization. The AuNP/C nanocomposite was characterized using SEM, HAADF-STEM electron tomography and electrochemical techniques, revealing a very large electroactive surface area (EASA). The figure shows the HAADF-STEM image (a) and the respective EDX elemental distribution (b) for the AuNP/C composite with 9.3 % Au-loading developed in this work (Au is marked in red and C in green).

Abstract

A facile, “one-pot”, chemical approach to synthesize gold-based nanoparticles finely dispersed on porous activated carbon (Norit) was demonstrated in this work. The pH of the synthesis bath played a critical role in determining the optimal gold-carbon interaction, which enabled a successful deposition of the gold nanoparticles onto the carbon matrix with a maximized metal utilization of 93 %. The obtained AuNP/C nanocomposite was characterized using SEM, HAADF-STEM electron tomography and electrochemical techniques. It was found that the Au nanoparticles, with diameters between 5 and 20 nm, were evenly distributed over the carbon matrix, both inside and outside the pores. Electrochemical characterization indicated that the composite had a very large electroactive surface area (EASA), as high as 282.4 m² g_Au ⁻¹. By exploiting its very high EASA, the catalyst was intended to boost the productivity of glucaric acid in the electrooxidation of its precursor, gluconic acid. However, cyclic voltammetry experiments revealed a very limited reactivity towards gluconic acid oxidation, due to the spacial hindrance of gluconic acid molecule which prevented diffusion inside the catalyst nanopores. On the other hand, the as-synthesized nanocomposite promises to be effective towards the ORR, and might thus find potential application as anode catalyst for fuel cells as well as for the scalability of all those electrochemical reactions involving small molecules with high diffusivity and catalysed by noble metals (i. e. CO₂, CH₄, N₂, etc..).

Recent Progress on Carbon‐Based Electrocatalysts for Oxygen Reduction Reaction: Insights on the Type of Synthesis Protocols, Performances and Outlook Mechanisms

Posted on 7 September 2023 by

This review explores carbon-based catalysts for oxygen reduction (ORR) in acidic and alkaline electrolytes, focusing on their mechanism, performance modulation strategies such as functionalization engineering, and doping strategies. Carbon-based materials are cost-effective, highly conductive, and have a wide range of allotropes. However, no specific review distinguishes between ORR activity, mechanism, and fuel cell performance in acidic and alkaline media for carbon functionalized and doped nanomaterials. That aspect is outlined in this review.

Abstract

Due to their low cost, accessibility of resources, and improved stability and durability, carbon-based nanomaterials have attracted significant attention as cathode materials for oxygen reduction reactions. These materials also exhibit intrinsic physical and electrochemical features. However, their potential for use in fuel cells is constrained by low ORR activity and slow kinetics. Carbon nanomaterials can be functionalized and doped with heteroatoms to change their morphologies and generate a large number of oxygen reduction active sites to lessen the problems. Doping the carbon lattice with heteroatoms like N, S, and P and functionalizing the carbon structure with −OCH₃, −F, −COO⁻, −O⁻ are two of these modifications that can change specific properties of the carbon nanomaterials like expanding interlayer distance, producing a large number of active sites, and enhancing oxygen reduction activity. When compared to pristine carbon-based nanomaterials, these doped and functionalized carbon nanomaterials, including their composites, exhibit accelerated rate performance, outstanding stability, and higher methanol tolerance. This article summarizes the most recent developments in heteroatom-doped and functionalized carbon-based nanomaterials, covering different synthesis approaches, characterization methods, electrochemical performance, and oxygen reduction reaction mechanisms. As cathode materials for fuel cell technologies, the significance of heteroatom co-doping and transition metal heteroatom co-doping is also underlined.

Controlled Potential Electrolysis: Transition from Fast to Slow Regimes in Homogeneous Molecular Catalysis. Application to the Electroreduction of CO2 Catalyzed by Iron Porphyrin

Posted on 7 September 2023 by

The resting state of a homogeneous molecular catalyst during a controlled potential electrolysis depends on operational parameters (catalytic rate constant, cell dimensions and stirring rate). A formal description is given and illustrated through the electroreduction of CO₂ catalyzed by Iron porphyrin switching from fast (confined catalysis) to slow (bulk catalysis) regimes.

Abstract

Molecular catalysis of electrochemical reactions is a field of intense activity because of the current interest in electrifying chemical transformations, including both electrosynthesis of organic molecules and production of fuels via small molecule activation. Controlled potential electrolysis (CPE) is often coupled with in situ in operando spectroscopic methods with the aim to gather mechanistic information regarding the catalytic species involved. Herein, considering a simple mechanism for a homogeneous molecular catalysis of an electrochemical reaction, we establish the concentration profile of the catalyst in the electrolysis cell enabling to envision the information that can be obtained from the coupling of this CPE with a spectroscopic probe in the cell compartment. We show how the characteristic parameters of the system (catalytic rate constant, cell dimensions and stirring rate) affect the response with particular emphasis on the transition between two limiting cases, namely a ‘fast’ catalysis regime where catalysis only takes place in a small layer adjacent to the electrode surface and a ‘slow’ catalysis regime where catalysis takes place in the bulk of the solution. These formal concepts are then illustrated with an experimental example, the electroreduction of CO₂ in dimethylformamide homogeneously catalyzed by iron tetraphenylporphyrin and followed by UV-vis spectroscopy.

Water‐Abundant Electrolytes: Towards Safer and Greener Aqueous Zinc‐Metal Batteries

Posted on 7 September 2023 by nLong Qian, nRui Yao, nCheng Yangn

This concept article aims to emphasize how to fabricate green and safe water-abundant Zn metal batteries. Several typical and advanced strategies towards water-abundant electrolyte systems are reviewed. We hope to arouse the attention of researchers for safer and greener aqueous Zn metal batteries when a large amount of toxic or expensive non-aqueous components are added into electrolytes.

Abstract

Aqueous Zn metal batteries have been regarded as promising candidates as an alternative to Li-ion batteries in large-scale energy storage systems due to their low-cost, safe and environmentally benign advantages. However, because of the introduction of solvent water, several problems, for example dendrites, parasite reactions, hydrogen evolution, and so on, are brought into aqueous Zn metal batteries. Regrettably, when trying to solve these problems, most efforts have taken the form of adding a large amount of non-aqueous components, which are usually harmful to the environment and not conducive to greener and safer aqueous batteries. In this Concept, we will introduce several electrolyte systems and mainly focus on how to build a water-abundant electrolyte with fewer non-aqueous components. This work will review the literature and offer instructive guidance for environmentally benign Zn metal batteries.

Sodium Tetrakis(hexafluoroisopropyloxy)aluminates: Synthesis and Electrochemical Characterisation of a Room‐Temperature Solvated Ionic Liquid

Posted on 4 September 2023 by

Ionic liquids: Weakly coordinating anions find ubiquitous use in chemistry. This work details the synthesis of sodium tetrakis(hexafluoroisopropyloxy)aluminate, which when solvated by one dimethoxyethane solvent molecule forms a room-temperature solvated ionic liquid. Thermal and electrochemical studies have been performed on this salt and its use an electrolyte for sodium-ion batteries explored.

Abstract

Weakly coordinating anions (WCAs) are used throughout chemistry to minimise cation-anion interactions in the solid and solution states. The ability to suppress ion-pairing has important bearings - or impacts on the properties of materials, on single-site catalysis and on ionic conductivity. Fluorinated alkoxy aluminates (containing [Al(OR^F)₄]⁻ anions) are an attractive class of WCA owing to their high thermodynamic stability, stemming from strong aluminium-oxygen bonds, and the ability to tailor their steric and electronic properties by changing the organic substituents (R). This work explores the structural and electrochemical properties of sodium tetrakis(hexafluoroisopropyloxy)aluminate, Na[Al(hfip)₄] ⋅ xDME (hfip=hexafluoroisopropyloxy, OⁱPr^F, DME=1,2-dimethoxyethane, x=3 or 1). When solvated with one DME molecule, Na[Al(hfip)₄] ⋅ DME is a room-temperature solvated ionic liquid, with an activation energy of conduction of 0.4 eV. Both Na[Al(hfip)₄] ⋅ 3DME and Na[Al(hfip)₄] ⋅ DME have been studied as electrolyte salts for sodium-ion batteries, where sodium-ion cycling proceeds but with low capacity retention.

Laser‐Assisted Interfacial Engineering for High‐Performance All‐Solid‐State Batteries

Posted on 4 September 2023 by

Laser-assisted interfacial engineering for improving the stability of all-solid-state batteries: The recent achievements of ultrafast pulsed laser ablation, selective laser sintering, laser-induced interlayers, and pulsed laser deposition technologies resulting in stable interfaces in SSB full cells have been reviewed. This review outlines underlying photophysical and electrochemical mechanisms for the enhanced stabilities of laser-processed SSB full cells. It provides insights into future research on the laser-assisted manufacturing of high-performance SSBs.

Abstract

Safe and high-energy-density solid-state batteries (SSBs) are promising candidates for use as the primary power source of next-generation electric vehicles. However, their poor rate capabilities and long-term cyclabilities because of material and interfacial instabilities have hindered their widespread commercialization. This study reviewed the recent progress of laser-assisted interfacial engineering technologies to address the stability issues at the interfaces of SSBs. First, the overview of the interfacial issues of SSBs is briefly outlined. Subsequently, the recent achievements are summarized according to the photophysical mechanisms of laser processing and the type of interfaces to which they are applied. Consequently, the critical laser processing factors to improve the interfacial stabilities of SSBs are highlighted in detail. Finally, the future challenges and opportunities in laser-assisted interfacial engineering for manufacturing high-performance SSBs have been discussed to provide guidelines for developing reliable and scalable processes.

High Salt Electrolyte Solutions Challenge the Electrochemical CO2 Reduction Reaction to Formate at Indium and Tin Cathodes

Posted on 4 September 2023 by nAykut Kas, nPaniz Izadi, nFalk Harnischn

Electrochemical feeding of salt-loving microorganisms: Halophilic microorganisms are promising for bioproduction from formate. Electrochemical CO₂ reduction to formate necessitates high reaction kinetics, selectivity, and overall efficiency in saline conditions. Starting from a growth media for halophiles adjusting the concentration and composition of salts and buffers in electrolyte solutions enabled higher electrochemical production of formate.

Abstract

Formate is a promising product of the electrochemical CO₂ reduction reaction (eCO₂RR) that can serve as feedstock for biological syntheses. Indium (In) has been shown as a selective electrocatalyst of eCO₂RR with high coulombic efficiency (CE) for formate production at small scale at biocompatible non-halophilic that is low salt conditions. Ohmic losses and challenges on potential/current distribution arise for scaling-up, where higher salt loads are advantageous for minimizing these. Higher salt concentration within the solution or halophilic conditions also enable the use of halophilic biocatalysts. We optimized eCO₂RR with halophilic media by introducing tin (Sn) as a more sustainable alternative to In. At 3 % NaCl providing a catholyte conductivity ( of 70 mS cm⁻¹, the maximum specific formate production rates (r _formate) of 0.143±0.030 mmol cm⁻² h⁻¹ and 0.167±0.027 mmol cm⁻² h⁻¹ were achieved at In and Sn electrocatalysts, respectively. Decrease in r _formate and CE, in addition to higher variation between replicates was observed with further increase in NaCl concentration above 3 % ( >70 mS cm⁻¹) up to 10 % ( =127 mS cm⁻¹). This study sets the foundation for integrated microbial synthesis by halophiles.

Bioengineered Lactate Oxidase Mutants for Enhanced Electrochemical Performance at Acidic pH

Posted on 1 September 2023 by

Lactate oxidase was engineered by site-directed mutagenesis to improve the biosensor performance for lactate detection at low pH. After rational design to modulate the pKa of the catalytic His 265, the S175A variant showed higher sensitivity than the lacerate oxidase wild-type.

Abstract

Electrochemical lactate biosensors based on lactate oxidase (LOx) are used for diagnostics, sports medicine, and the food industry. However, samples from these sectors may have acidic levels at which the biocatalytic activity of LOx may be diminished. In this work, the enhancement of the bio-electrocatalytic activity of LOx at low pH by pKa modulation of its catalytic His265 was studied by rational engineering of lactate oxidase from Aerococcus viridans (AvLOx). Several candidates based on interactions with His265 were selected by in silico structural analysis. The designed variants were heterologously produced, and the S175A mutant showed considerable improvement over its wild-type counterpart, showing 157 % of the enzymatic activity found in the wild-type at pH 5. Bioelectrodes were assembled based on Prussian-blue-modified carbon paper mediator system. The electrocatalytic performance of the amperometric biosensors of S175A variant at pH 5 exhibited a linear range of 0.2–2 mM measured at 0 V vs SCE, a sensitivity of −17.52 μA/mM ⋅ cm², representing 240 % of the sensitivity found in the wild-type biosensor, and a limit of detection of 38 μM, lower than observed with the wild-type enzyme. These results show that the mutant obtained offers a significant improvement in lactate biosensing at low pH.