Self-Supported PdxBi Catalysts for the Electrooxidation of Glycerol in Alkaline Media

Surface-Enriched Single-Bi-Atoms Tailoring of Pt Nanorings for Direct Methanol Fuel Cells with Ultralow-Pt-Loading

Single-atom decorating of Pt emerges as a highly effective strategy to boost catalytic properties, which can trigger the most Pt active sites while blocking the smallest number of Pt atoms. However, the rational design and creation of high-density single-atoms on Pt surface remain as a huge challenge. Herein, a customized synthesis of surface-enriched single-Bi-atoms tailored Pt nanorings (SE-Bi1/Pt NRs) toward methanol oxidation is reported, which is guided by the density functional theory (DFT) calculations suggesting that a relatively higher density of Bi species on Pt surface can ensure a CO-free pathway and accelerate the kinetics of *HCOOH formation. Decorating Pt NRs with dense single-Bi-atoms is achieved by starting from PtBi intermetallic nanoplates (NPs) with intrinsically isolated Bi atoms and subsequent etching and annealing treatments. The SE-Bi1/Pt NRs exhibit a mass activity of 23.77 A mg-1 Pt toward methanol oxidation in alkaline electrolyte, which is 2.2 and 12.8 times higher than those of Pt-Bi NRs and Pt/C, respectively. This excellent activity endows the SE-Bi1/Pt NRs with a high likelihood to be used as a practical anodic electrocatalyst for direct methanol fuel cells （DMFCs） with high power density of 85.3 mW cm-2 and ultralow Pt loading of 0.39 mg cm-2.

Selective glucose electro-oxidation catalyzed by TEMPO on graphite felt

Long-term electrolyses of glucose in a potassium carbonate (K2CO3) aqueous electrolyte have been performed on graphite felt electrodes with TEMPO as a homogeneous catalyst. The influences of the operating conditions (initial concentrations of glucose, TEMPO, and K2CO3 along with applied anode potential) on the conversion, selectivity toward gluconate/glucarate, and faradaic efficiency were assessed first. Then, optimizations of the conversion, selectivity, and faradaic efficiency were performed using design of experiments based on the L9 (34) Taguchi table, which resulted in 84% selectivity toward gluconate with 71% faradaic efficiency for up to 79% glucose conversion. Side products such as glucaric acid were also obtained when the applied potential exceeded 1.5 V vs. reversible hydrogen electrode.

Regulation of Catalyst Immediate Environment Enables Acidic Electrochemical Benzyl Alcohol Oxidation to Benzaldehyde

Electrocatalytic alcohol oxidation in acid offers a promising alternative to the kinetically sluggish water oxidation reaction toward low-energy H2 generation. However, electrocatalysts driving active and selective acidic alcohol electrochemical transformation are still scarce. In this work, we demonstrate efficient alcohol-to-aldehyde conversion achieved by reticular chemistry-based modification of the catalyst's immediate environment. Specifically, coating a Bi-based electrocatalyst with a thin layer of metal-organic framework (MOF) substantially improves its performance toward benzyl alcohol electro-oxidation to benzaldehyde in a 0.1 M H2SO4 electrolyte. Detailed analysis reveals that the MOF adlayer influences catalysis by increasing the reactivity of surface hydroxides as well as weakening the catalyst-benzaldehyde binding strength. In turn, low-potential (0.65 V) cathodic H2 evolution was obtained through coupling it with anodic benzyl alcohol electro-oxidation. Consequently, the presented approach could be implemented in a wide range of electrocatalytic oxidation reactions for energy-conversion application.

Synergistic Lewis and Brønsted Acid Sites Promote OH* Formation and Enhance Formate Selectivity: Towards High-efficiency Glycerol Valorization

As a sustainable valorization route, electrochemical glycerol oxidation reaction (GOR) involves in formation of key OH* and selective adsorption/cleavage of C-C(O) intermediates with multi-step electron transfer, thus suffering from high potential and poor formate selectivity for most non-noble-metal-based electrocatalysts. So, it remains challenging to understand the structure-property relationship as well as construct synergistic sites to realize high-activity and high-selectivity GOR. Herein, we successfully achieve dual-high performance with low potentials and superior formate selectivity for GOR by forming synergistic Lewis and Brønsted acid sites in Ni-alloyed Co-based spinel. The optimized NiCo oxide solid-acid electrocatalyst exhibits low reaction potential (1.219 V@10 mA/cm2) and high formate selectivity (94.0 %) toward GOR. In situ electrochemical impedance spectroscopy and pH-dependence measurements show that the Lewis acid centers could accelerate OH* production, while the Brønsted acid centers are proved to facilitate high-selectivity formation of formate. Theoretical calculations reveal that NiCo alloyed oxide shows appropriate d-band center, thus balancing adsorption/desorption of C-O intermediates. This study provides new insights into rationally designing solid-acid electrocatalysts for biomass electro-upcycling.

Electrocatalytic Oxidation of Methanol and Ethanol with 3d-Metal Based Anodic Electrocatalysts in Alkaline Media Using Carbon Based Electrode Assembly

Homogeneous electrocatalytic systems based on readily available, earth-abundant, inexpensive base metals Ni, Co, and Cr have been formulated for the electro-oxidation of alcohols (methanol and ethanol) that constitute a key half-cell component of direct alcohol fuel cells (DAFCs). Notably, excellent results were obtained for both methanol as well as ethanol electro-oxidation while operating with a half-cell assembly based on all-non-noble working and counter electrode systems consisting of glassy carbon and graphite rod, respectively. Using NaOH as the supporting electrolyte, Ni/Co/Cr metal salts and their bis(iminopyridine) complexes have been used as anodic electrocatalysts for the alcohol half-cell reactions, and among them, catalytic systems based on Co outperformed the corresponding systems based on Ni and Cr. The system comprising CoCl2.·6H2O [10 mM] + NaOH [6 M] at room temperature emerged as the best electrocatalyst for both methanol [5 M] electro-oxidation (ca. 522.5 ± 13.5 mA cm-2 at 1.4 V) and ethanol [5 M] electro-oxidation (ca. 209 ± 25 mA cm-2 at 1.34 V). It was observed that regardless of the starting alcohol, the end product is carbon dioxide, all of which gets trapped as sodium carbonate (up to 97% yield), thereby mitigating any possible hazards of greenhouse gas emission. Inferences obtained from FETEM, FESEM, and EDS analysis of both the electrolyte solution and residues deposited on the electrode surface provide evidence for the mostly homogeneous nature of the reaction mixture with the molecular catalyst being the major contributor toward the electrocatalytic activity apart from the minor role played by trace heterogeneous particles. The current cell assembly operating with non-noble working and counter electrodes utilizing a catalytic system based on an earth-abundant, base metal salt/complex that not only results in good half-cell current densities for high-energy power-source DAFCs but also generates high-value sodium carbonate offers an exciting avenue.

Electrodeposition-Assisted Crystal Growth Regulation of PdBi Clusters on Carbon Cloths for Ethanol Oxidation

Carbon-supported Pd-based clusters are one of the most promising anodic catalysts for ethanol oxidation reaction (EOR) due to their encouraging activity and practical applications. However, unclear growth mechanism of Pd-based clusters on the carbon-based materials has hindered their extensive applications. Herein, we first introduce multi-void spherical PdBi cluster/carbon cloth (PdBi/CC) composites by an electrodeposition routine. The growth mechanism of PdBi clusters on the CC supports has been systemically investigated by evaluating the selected samples and tuning their compositions, which involve the big difference in standard redox potential between Pd2+/Pd and Bi3+/Bi and easy adsorption of Bi3+ on the surface of Pd-rich seeds. Benefitting from the ensembles of many nanocrystal subunits, multi-void spherical PdBi clusters can present collective properties and novel functionalities. In addition, the outstanding characteristics of CC supports enable PdBi clusters with stable nanostructures. Thanks to the unique structure, Pd20Bi/CC catalysts manifest higher EOR activity and better stability compared to Pd/CC. Systematic characterizations and a series of CO poisoning tests further confirm that the dramatically enhanced EOR activity and stability can be attributed to the incorporation of Bi species and the strong coupling of the structure between PdBi clusters and CC supports.

Solid-State Nanopore Array: Manufacturing and Applications

Nanopore brings extraordinary properties for a variety of potential applications in various industrial sectors. Since manufacturing of solid-state nanopore is first reported in 2001, solid-state nanopore has become a hot topic in the recent years. An increasing number of manufacturing methods have been reported, with continuously decreased sizes from hundreds of nanometers at the beginning to ≈1 nm until recently. To enable more robust, sensitive, and reliable devices required by the industry, researchers have started to explore the possible methods to manufacture nanopore array which presents unprecedented challenges on the fabrication efficiency, accuracy and repeatability, applicable materials, and cost. As a result, the exploration of fabrication of nanopore array is still in the fledging period with various bottlenecks. In this article, a wide range of methods of manufacturing nanopores are summarized along with their achievable morphologies, sizes, inner structures for characterizing the main features, based on which the manufacturing of nanopore array is further addressed. To give a more specific idea on the potential applications of nanopore array, some representative practices are introduced such as DNA/RNA sequencing, energy conversion and storage, water desalination, nanosensors, nanoreactors, and dialysis.

Environment-Friendly Ascorbic Acid Fuel Cell

Recently, ascorbic acid (AA) has been studied as an environment-friendly fuel for energy conversion devices. This review article has deliberated an overview of ascorbic acid electrooxidation and diverse ion exchange types of AA-based fuel cells for the first time. Metal and carbon-based catalysts generated remarkable energy from environment-friendly AA fuel. The possibility of using AA in a direct liquid fuel cell (DLFC) without emitting any hazardous pollutants is discussed. AA fuel cells have been reviewed based on carbon nanomaterials, alloys/bimetallic nanoparticles, and precious and nonprecious metal nanoparticles. Finally, the obstacles and opportunities for using AA-based fuel cells in practical applications have also been incorporated.

Ultra-Low Content Bismuth-Anchored Gold Aerogels with Plasmon Property for Enhanced Nonenzymatic Electrochemical Glucose Sensing

Effective glucose surveillance provides a strong guarantee for the high-quality development of human health. Au nanomaterials possess compelling applications in nonenzymatic electrochemical glucose biosensors owing to superior catalytic performances and intriguing biocompatibility properties. However, it has been a grand challenge to accurately control the architecture and composition of Au nanomaterials to optimize their optical, electronic, and magnetic properties for further improving the performance of electrocatalytic sensing. Herein, ultra-low content Bi-anchored Au aerogels are synthesized via a one-step reduction strategy. Benefiting from the unique structure of aerogels as well as the synergistic effect between Au and Bi, the optimized Au₂₀₀Bi aerogels greatly boost the activity of glucose oxidation compared with Au aerogels. Under plasmon resonance excitation, bimetallic Au₂₀₀Bi aerogels with wider photics-dependent properties further show plasmon-promoted glucose electro-oxidation activity, which is derived from the photothermal and photoelectric effects caused by the local surface plasmon resonance. Thanks to the enhanced performance, a nonenzymatic electrochemical glucose biosensor is constructed to detect glucose with high sensitivity. This plasmon-promoted electrocatalytic activity through the synergetic strategy of bimetallic aerogels has potential applications in various research fields.

Activated Ni-OH Bonds in a Catalyst Facilitates the Nucleophile Oxidation Reaction

The nucleophile oxidation reaction (NOR) is of enormous significance for organic electrosynthesis and coupling for hydrogen generation. However, the nonuniform NOR mechanism limits its development. For the NOR, involving electrocatalysis and organic chemistry, both the electrochemical step and non-electrochemical process should be taken into account. The NOR of nickel-based hydroxides includes the electrogenerated dehydrogenation of the Ni²⁺ -OH bond and a spontaneous non-electrochemical process; the former determines the electrochemical activity, and the nucleophile oxidation pathway depends on the latter. Herein, the space-confinement-induced synthesis of Ni₃ Fe layered double hydroxide intercalated with single-atom-layer Pt nanosheets (Ni₃ Fe LDH-Pt NS) is reported. The synergy of interlayer Pt nanosheets and multiple defects activates Ni-OH bonds, thus exhibiting an excellent NOR performance. The spontaneous non-electrochemical steps of the NOR are revealed, such as proton-coupled electron transfer (PCET; Ni³⁺ -O + X-H = Ni²⁺ -OH + X^• ), hydration, and rearrangement. Hence, the reaction pathway of the NOR is deciphered, which not only helps to perfect the NOR mechanism, but also provides inspiration for organic electrosynthesis.

Supercritical Fluid-Assisted Fabrication of Pd Nanoparticles/Graphene Using a Choline Chloride-Oxalic Acid Deep Eutectic Solvent for Enhancing the Electrochemical Oxidation of Glycerol

A green method for synthesizing Pd nanoparticles/graphene composites from a choline chloride-oxalic acid deep eutectic solvent (DES) without a reducing agent or a surfactant is reported. Deep eutectic solvents are usually composed of halide salts and hydrogen-bond donors, and many are biocompatible and biodegradable. The merits of deep eutectic solvents include that they serve as reducing agents and dispersants, and Pd nanoparticles are tightly anchored to graphene. The size and dispersion of Pd particles are improved when supercritical carbon dioxide (scCO₂) is used because it has gaslike diffusivity and near-zero surface tension, which results in excellent wettability between the scCO₂ and the carbon surface. The prepared sc-Pd NPs/GR/SPCE shows excellent activity toward glycerol oxidation compared to composites not fabricated by scCO₂ processes. This study demonstrates the potential of using this scCO₂-assisted protocol combined with deep eutectic solvents to further construct nanoparticles/graphene composites.

Pyrenecarboxaldehyde encapsulated porous TiO2 nanoreactors for monitoring cellular GSH levels

Recently, ternary electrochemiluminescence (ECL) system has become a hot research topic due to its great potential for improving ECL efficiency by promoting the generation of intermediates. However, it is still a great challenge to increase the utilization rate of intermediates in a ternary ECL system. Herein, we propose a strategy to increase the utilization rate of intermediates by designing pyrenecarboxaldehyde (Pyc) encapsulated porous titania (pTiO₂) nanospheres (Pyc@pTiO₂) as ECL nanoreactors for an integrated ternary (luminophore/coreactant/co-reaction accelerator, Pyc/S₂O₈^2-/TiO₂) ECL system construction. Specifically, pTiO₂ acted as an ECL co-reaction accelerator, in which Pyc could obtain electrons from the conduction band of TiO₂ to produce more SO₄˙^-, increasing its emissions. Simultaneously, pTiO₂ could provide confined reaction spaces to effectively shorten the diffusion distance, extend the lifetime of free radicals, increase the utilization rate of intermediates and improve the efficiency of the ternary ECL system. As a proof of concept, the Pyc@pTiO₂ nanoreactors-based sensing platform was successfully constructed to sensitively monitor cellular GSH levels. Overall, this work for the first time proposed an avenue to increase the utilization rate of intermediates in a ternary ECL system, which opened a new route for ECL biosensing in cell analysis applications.

Selective Photoelectrocatalytic Glycerol Oxidation to Dihydroxyacetone via Enhanced Middle Hydroxyl Adsorption over a Bi2O3-Incorporated Catalyst

Photoelectrocatalytic (PEC) glycerol oxidation offers a sustainable approach to produce dihydroxyacetone (DHA) as a valuable chemical, which can find use in cosmetic, pharmaceutical industries, etc. However, it still suffers from the low selectivity (≤60%) that substantially limits the application. Here, we report the PEC oxidation of glycerol to DHA with a selectivity of 75.4% over a heterogeneous photoanode of Bi₂O₃ nanoparticles on TiO₂ nanorod arrays (Bi₂O₃/TiO₂). The selectivity of DHA can be maintained at ∼65% under a relatively high conversion of glycerol (∼50%). The existing p-n junction between Bi₂O₃ and TiO₂ promotes charge transfer and thus guarantees high photocurrent density. Experimental combined with theoretical studies reveal that Bi₂O₃ prefers to interact with the middle hydroxyl of glycerol that facilitates the selective oxidation of glycerol to DHA. Comprehensive reaction mechanism studies suggest that the reaction follows two parallel pathways, including electrophilic OH* (major) and lattice oxygen (minor) oxidations. Finally, we designed a self-powered PEC system, achieving a DHA productivity of 1.04 mg cm^-2 h^-1 with >70% selectivity and a H₂ productivity of 0.32 mL cm^-2 h^-1. This work may shed light on the potential of PEC strategy for biomass valorization toward value-added products via PEC anode surface engineering.

Synthesis of PtRu alloy nanofireworks as effective catalysts toward glycerol electro-oxidation in alkaline media

Electro-oxidation of glycerol is a key anodic reaction in direct alcohol fuel cell (DAFCs). Exploring the cost-effective nanocatalysts for glycerol oxidation reaction (GOR) is very important for the development of DAFC, but it is still challenging. In this paper, nanofirework-like PtRu alloy catalyst was successfully synthesized and used for GOR in alkaline medium. Thanks to the unique nanofirework-like structure and synergetic effects, the activity and stability of the as-prepared PtRu alloy nanofireworks (NFs) toward GOR were significantly improved relative to Pt NFs. In particular, the peak current density of GOR catalyzed by the optimized Pt₁Ru₃ NFs catalyst reached 2412.0 mA mg^-1, surpassing that of commercial Pt/C catalyst. This work has important guidance for the design of advanced anode electrocatalysts for fuel cells.

A novel Bismuth hydroxide (Bi(OH)3) semiconductor with highly-efficient photocatalytic activity

Herein, a novel Bi(OH)3 photocatalyst was successfully synthesized. Benefiting from the suitable band positions, abundant alkaline groups and oxygen vacancies, the as-prepared semiconductor exhibits efficient activity in both photocatalytic CO2...

Alloyed Palladium-Lead Nanosheet Assemblies for Electrocatalytic Ethanol Oxidation

Synthesizing alloyed bimetallic electrocatalysts with a three-dimensional (3D) structure assembly have arouse great interests in electrocatalysis. We synthesized a class of alloyed Pd₃Pb/Pd nanosheet assemblies (NSAs) composed of a two-dimensional (2D) sheet structure with adjustable compositions via an oil bath approach at a low temperature. Both the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the successful formation of the nanosheet structure, where the morphology of Pd₃Pb/Pd NSAs can be regulated by adjusting the atomic mole ratio of Pb and Pb metal precursors. The power X-ray diffraction (XRD) pattern shows that Pd₃Pb/Pd NSA catalysts are homogeneously alloyed. Electrochemical analysis and the density functional theory (DFT) method demonstrate that the electrocatalytic activity of the alloyed Pd₃Pb/Pd NSAs can be improved by the doping of the Pb element. As a result of the addition of element Pb and change of the electron structure, the electrocatalytic activity toward ethanol oxidation of alloyed Pd₃Pb/Pd-15 NSA can reach up to 2886 mA mg^-1, which is approximately 2.8 times that of the pure Pd NSA counterpart (1020 mA mg^-1). The Pd₃Pb/Pd NSAs are favorable in a high catalytic temperature, high KOH concentration, and high ethanol concentration.

Bifunctional effect of Bi(OH)3 on the PdBi surface as interfacial Brønsted base enables ethanol electro-oxidization

Palladium (Pd) is supposed to be one of the most promising catalytic metals towards ethanol (C₂H₅OH) oxidation reaction (EOR). However, Pd electrocatalysts easily suffer from the poisoning of the intermediates (especially CO), resulting in the quick decay of EOR catalysis. Herein, inspired by the Brønsted-Lowry acid-base theory, a "attraction-repulsion" concept is proposed to guide the surface structure engineering toward EOR catalysts. Specifically, we induce Bi(OH)₃ species as Brønsted base onto PdBi nanoplates to effectively repel the adsorption of CO intermediates. The PdBi-Bi(OH)₃ nanoplates show an impressive mass activity of 4.46 A mg_Pd^-1 during the EOR catalysis and keep excellent stability. Both the stability and enhanced performance are attributed by the interfacial Brønsted base Bi(OH)₃ which can selectively attract and repel reactants and intermediates, as evidenced from in situ measurements and theoretical views.

An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au

In the most recent decade, glycerol electrooxidation (GEOR) has attracted extensive research interest for valorization of glycerol: the conversion of glycerol to value-added products. These reactions at platinum, palladium, and gold electrodes have a lot of uncertainty in their reaction mechanisms, which has generated some controversies. This review gathers many reported experimental results, observations and proposed reaction mechanisms in order to draw a full picture of GEOR. A particular focus is the clarification of two propositions: Pd is inferior to Pt in cleaving the C-C bonds of glycerol during the electrooxidation and the massive production of CO₂ at high overpotentials is due to the oxidation of the already-oxidized carboxylate products. It is concluded that the inferior C-C bond cleavability with Pd electrodes, as compared with Pt electrodes, is due to the inefficiency of deprotonation, and the massive generation of CO₂ as well as other C1/C2 side products is partially caused by the consumption of OH^- at the anodes, as a lower pH reduces the amount of carboxylates and favors the C-C bond scission. A reaction mechanism is proposed in this review, in which the generation of side products are directly from glycerol ("competition" between each side product) rather than from the further oxidation of C2/C3 products. Additionally, GEOR results and associated interpretations for Ni electrodes are presented, as well as a brief review on the performances of multi-metallic electrocatalysts (most of which are nanocatalysts) as an introduction to these future research hotpots.

Recent Progress of Ultrathin 2D Pd-Based Nanomaterials for Fuel Cell Electrocatalysis

Pd- and Pd-based catalysts have emerged as potential alternatives to Pt- and Pt-based catalysts for numerous electrocatalytic reactions, particularly fuel cell-related reactions, including the anodic fuel oxidation reaction (FOR) and cathodic oxygen reduction reaction (ORR). The creation of Pd- and Pd-based architectures with large surface areas, numerous low-coordinated atoms, and high density of defects and edges is the most promising strategy for improving the electrocatalytic performance of fuel cells. Recently, 2D Pd-based nanomaterials with single or few atom thickness have attracted increasing interest as potential candidates for both the ORR and FOR, owing to their remarkable advantages, including high intrinsic activity, high electron mobility, and straightforward surface functionalization. In this review, the recent advances in 2D Pd-based nanomaterials for the FOR and ORR are summarized. A fundamental understanding of the FOR and ORR is elaborated. Subsequently, the advantages and latest advances in 2D Pd-based nanomaterials for the FOR and ORR are scientifically and systematically summarized. A systematic discussion of the synthesis methods is also included which should guide researchers toward more efficient 2D Pd-based electrocatalysts. Lastly, the future outlook and trends in the development of 2D Pd-based nanomaterials toward fuel cell development are also presented.

Facet-Dependent Long-Term Stability of Gold Aerogels toward Ethylene Glycol Oxidation Reaction

In this work, a series of Au_PNR^6 - 50 aerogels with different percentages of {110} facets (from ∼12 to 36%) were controllably prepared and then used to investigate their performance (specific activity and long-term stability) toward ethylene glycol oxidation reaction (EGOR), in which PNR represents the particle number ratio of 6 nm Au NPs to 50 nm Au NPs. It is found that their specific activity and long-term stability highly depend on the sum of the percentage of the {100} and {111} facets and the percentage of {110} facets, respectively. In addition, Au₂₄^6 - 50 aerogels with the highest percentage of {110} facets can possess excellent long-term stability (retaining about 95% of the initial current) but still have excellent specific activity (about 90.42 mA cm^-2). Thus, the specific activity and long-time stability of Au_PNR^6 - 50 aerogels toward EGOR can be well balanced by controlling the proper percentage of {110} facets on their surfaces. Therefore, the successful fabrication of Au_PNR^6 - 50 aerogels with greatly improved long-term stability and excellent specific activity not only provides a novel method for the design of electrocatalysts but also would boost the commercial development of direct ethylene glycol fuel cells.

Operando vibrational spectroscopy for electrochemical biomass valorization

Electrocatalysis is a promising route to generate fuels and value-added chemicals from abundant feedstocks powered by renewable electricity. The field of electrocatalysis research has made great progress in supplementing electrocatalyst development with operando vibrational spectroscopic techniques, those carried out simultaneously as the reaction is occurring. Such experiments unveil reaction mechanisms, structure-activity relationships and consequently, accelerate the development of next generation electrocatalytic systems. While operando techniques have now been extensively applied to water electrolysis and CO2 reduction, their application to the emerging area of biomass valorization is rather nascent. The electrocatalytic conversion of biomass can provide an alternate, environmentally friendly route to the chemicals which power our society, but this field still requires much growth before the envisioned technologies are economically competetive with thermochemical routes. Within this context, a growing body of work has begun to translate the methodology and concepts from water/CO2 electrolysis to biomass valorization to elucidate links between catalyst structure, adsorbed surface intermediates, and the resultant catalytic performance. The reactions of interest here include the upgrading of biomass platforms such a 5-hydroxymethylfurfural or glycerol to value-added chemicals. In this feature article we highlight these efforts and provide a critical view on the steps necessary to take to further progress the field. We further show how the knowledge derived from these studies can be translated to a plethora of other organic transformations to forge new avenues in renewable energy electrocatalysis.

Stable and active Pt colloid preparation by modified citrate reduction and a mechanism analysis of inorganic additives

Ultra-small and monodispersed Pt nanoparticles (NPs) have been successfully synthesized in polymer electrolyte membrane fuel cells. The process normally involves the use of capping agents, organic species, templates, and substrates and is thus complex. Hence, obtaining Pt NPs with a clean surface is challenging. In this study, a method for preparing stable and highly dispersed Pt NPs with clean surfaces is proposed. The method involves the use of a modified Na₃C₆H₅O₇ reduction process assisted by NaNO₃ stabilization. The specific complexations of NO₂^- ions possibly alter the reaction kinetics and lower the growth rate of Pt NPs by retarding the reduction reaction. The optimized Pt/carbon nanotube (CNT) catalysts exhibit high mass activity and moderate activity decay after 10,000 times of potential cycling compared with commercially available Pt/C catalysts. Then, membrane electrode assemblies based on the resultant catalysts are characterized. The cell performance of 744 mW cm^-2 (maximum power density) is achieved after the optimized Pt/CNT catalysts are used in carbon black.

Electroreforming of Glucose and Xylose in Alkaline Medium at Carbon Supported Alloyed Pd3Au7 Nanocatalysts: Effect of Aldose Concentration and Electrolysis Cell Voltage

The effects of cell voltage and of concentration of sugars (glucose and xylose) on the performances of their electro-reforming have been evaluated at a Pd3Au7/C anode in 0.10 mol L−1 NaOH solution. The catalyst synthesized by a wet chemistry route is first comprehensively characterized by physicochemical and electrochemical techniques. The supported catalyst consists in alloyed Pd3Au7 nanoparticles of circa 6 nm mean diameter deposited on a Vulcan XC72 carbon support, with a metal loading close to 40 wt%. Six-hour chronoamperometry measurements are performed at 293 K in a 25 cm2 electrolysis cell for the electro-conversion of 0.10 mol L−1 and 0.50 mol L−1 glucose and xylose at cell voltages of +0.4 V, +0.6 V and +0.8 V. Reaction products are analyzed every hour by high performance liquid chromatography. The main products are gluconate and xylonate for glucose and xylose electro-reforming, respectively, but the faradaic yield, the selectivity and the formation rate of gluconate/xylonate decrease with the increase of aldose concentration, whereas lower faradaic yields and higher formation rates of gluconate/xylonate are observed at +0.8 V than at +0.4 V (higher chemical yields).

Prospects of Value-Added Chemicals and Hydrogen via Electrolysis

Cost is a major drawback that limits the industrial-scale hydrogen production through water electrolysis. The overall cost of this technology can be decreased by coupling the electrosynthesis of value-added chemicals at the anode side with electrolytic hydrogen generation at the cathode. This Minireview provides a directory of anodic oxidation reactions that can be combined with cathodic hydrogen generation. The important parameters for selecting the anodic reactions, such as choice of catalyst material and its selectivity towards specific products are elaborated in detail. Furthermore, various novel electrolysis cell architectures for effortless separation of value-added products from hydrogen gas are described.

Assessment of the beneficial combination of electrochemical and ultrasonic activation of compounds originating from biomass

The electro-oxidation of organic molecules at the anode with simultaneous generation of hydrogen at the cathode in electrosynthesis reactors is considered as a promising and efficient process for the co-production of hydrogen and bio-sourced value-added chemicals. In this study and for the first time, we investigated the electro-oxidation of glucose and methylglucoside in 0.1 mol L^-1 NaOH on polycrystalline Pt (real surface area = 14.5 ± 0.5 cm², roughness ≈ 5) in the potential range [0; +1.20 V vs. rhe] under silent and ultrasonic (bath, 45 kHz, P_acous = 11.20 W) conditions. A series of linear sweep voltammograms, chronoamperograms and high-performance liquid chronoamperograms were generated. It was found that higher current densities were obtained under ultrasonic conditions over the potential range of +0.25 V to +1.10 V vs. rhe, indicating that higher oxidation rates were provided under ultrasonication. It was observed that the desorption of species from the Pt surface in the medium potential region was favoured, allowing free catalytic Pt sites for further adsorption and oxidation of reactants; and in the high potential region, high peak current densities in the presence of ultrasound was due to enhanced mass transport of the electroactive species from the bulk electrolyte to the Pt-polycrystalline electrode surface. HPLC studies confirmed that higher electrochemical activity was obtained in the presence of ultrasound than in the absence. In our conditions, it was also found that low frequency ultrasound did not change the selectivity of the glucose and methylglucoside electro-oxidation reactions but instead, a significant increase in the rate of conversion was observed.

Electrochemical biomass valorization on gold-metal oxide nanoscale heterojunctions enables investigation of both catalyst and reaction dynamics with operando surface-enhanced Raman spectroscopy

The electrochemical oxidation of biomass platforms such as 5-hydroxymethylfurfural (HMF) to value-added chemicals is an emerging clean energy technology.

The electrochemical oxidation of biomass platforms such as 5-hydroxymethylfurfural (HMF) to value-added chemicals is an emerging clean energy technology. However, mechanistic knowledge of this reaction in an electrochemical context is still lacking and operando studies are even more rare. In this work, we utilize core–shell gold-metal oxide nanostructures which enable operando surface-enhanced Raman spectroelectrochemical studies to simultaneously visualize catalyst material transformation and surface reaction intermediates under an applied voltage. As a case study, we show how the transformation of NiOOH from ∼1–2 nm amorphous Ni layers facilitates the onset of HMF oxidation to 2,5-furandicarboxylic acid (FDCA), which is attained with 99% faradaic efficiency in 1 M KOH. In contrast to the case in 1 M KOH, NiOOH formation is suppressed, and consequently HMF oxidation is sluggish in 10 mM KOH, even at highly oxidizing potentials. Operando Raman experiments elucidate how surface adsorption and interaction dictates product selectivity and how the surface intermediates evolve with applied potential. We further extend our methodology to investigate NiFe, Co, Fe, and CoFe catalysts and demonstrate that high water oxidation activity is not necessarily correlated with excellent HMF oxidation performance and highlight catalytic factors important for this reaction such as reactant–surface interactions and the catalysts' physical and electronic structure. The insights extracted are expected to pave the way for a deepened understanding of a wide array of electrochemical systems such as for organic transformations and CO₂ fixation.

Nanoscale engineering of porous Fe-doped Pd nanosheet assemblies for efficient methanol and ethanol electrocatalyses

Although great successes have been accomplished on the controlled synthesis of 2D and 3D Pd-containing nanomaterials, tapping into the novel Pd-containing electrocatalysts that combined the advantages of both 2D and 3D structures remains a significant challenge. Here, an approach to systematically produce porous Fe-doped Pd nanosheet assemblies (NSAs) with a geometry tuning from PdFe hollow nanospheres (HNSs), PdFe nanocages (NCs), to PdFe nanoplates (NPs) is reported. The inherent ultrathin and porous features endow these PdFe catalysts with excellent electrocatalytic performance. As a result, the optimized 3D PdFe NCs show a much-improved methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) activities in comparison with PdFe HNSs, Pd NPs, and commercial Pd/C catalysts. Moreover, these PdFe nanocatalysts also display greatly enhanced electrocatalytic stability, which can endure 500 cycles with negligible activity loss and structural changes. The mechanism investigations reveal that the introduced Fe atom efficiently modulates the electronic structure of Pd, leading to the downshift of the d-band center of Pd, which is beneficial for the adsorption of reactants. Moreover, the porous nanosheet assembly structure can provide rich mass and electron transfer channels, further boosting the improvement of electrocatalytic performance.

A review of recent progress on electrocatalysts toward efficient glycerol electrooxidation

Glycerol electrooxidation has attracted immense attention due to the economic advantage it could add to biodiesel production. One of the significant challenges for the industrial development of glycerol electrooxidation process is the search for a suitable electrocatalyst that is sustainable, cost effective, and tolerant to carbonaceous species, results in high performance, and is capable of replacing the conventional Pt/C catalyst. We review suitable, sustainable, and inexpensive alternative electrocatalysts with enhanced activity, selectivity, and durability, ensuring the economic viability of the glycerol electrooxidation process. The alternatives discussed here include Pd-based, Au-based, Ni-based, and Ag-based catalysts, as well as the combination of two or three of these metals. Also discussed here are the prospective materials that are yet to be explored for glycerol oxidation but are reported to be bifunctional (being capable of both anodic and cathodic reaction). These include heteroatom-doped metal-free electrocatalysts, which are carbon materials doped with one or two heteroatoms (N, B, S, P, F, I, Br, Cl), and heteroatom-doped nonprecious transition metals. Rational design of these materials can produce electrocatalysts with activity comparable to that of Pt/C catalysts. The takeaway from this review is that it provides an insight into further study and engineering applications on the efficient and cost-effective conversion of glycerol to value-added chemicals.

Recent advances in the electrooxidation of biomass-based organic molecules for energy, chemicals and hydrogen production

The recent developments in biomass-derivative fuelled electrochemical converters for electricity or hydrogen production together with chemical electrosynthesis have been reviewed.

Etching high-Fe-content PtPdFe nanoparticles as efficient catalysts towards glycerol electrooxidation

Great effort has been made to improve the activity and stability, as well as increase the utilization efficiency of noble metal-based electrocatalysts.

Three-dimensional PdCuM (M = Ru, Rh, Ir) Trimetallic Alloy Nanosheets for Enhancing Methanol Oxidation Electrocatalysis

Owing to their intrinsically high activity and rich active sites on the surface, noble metal materials with an ultrathin two-dimensional nanosheet structure are emerging as ideal catalysts for boosting fuel cell reactions. However, the realization of controllable synthesis of multimetallic Pd-based alloy ultrathin nanosheets (NSs) for achieving enhanced electrocatalysis evolved from compositional and structural advantages remains a grand challenge. Herein, we report a universal method for the construction of a new series of the three-dimensional (3D) multimetallic PdCuM (M = Ru, Rh, Ir) superstructures that consist of ultrathin alloy NSs. Different from the conventional 2D ultrathin nanostructure, the 3D PdCuM NSs that endowed with abundant routes for fast mass transport, high noble material utilization efficiency, and ligand effect from M to PdCu display large promotion in electrocatalytic performance for the methanol oxidation reaction. Impressively, the composition-optimized Pd₅₉Cu₃₃Ru₈ NSs, Pd₅₇Cu₃₄Rh₉ NSs, and Pd₆₃Cu₂₉Ir₈ NSs show the mass activities of 1660.8, 1184.4, and 1554.8 mA mg^-1 in alkaline media, which are 4.9, 3.5, and 4.6-fold larger than that of commercial Pd/C, respectively. More importantly, all of the PdCuM NSs are also very stable for long-term electrochemical tests.

Surface engineering of ultrasmall supported PdxBi nanoalloys with enhanced electrocatalytic activity for selective alcohol oxidation

Ultrasmall and homogeneous bimetallic PdxBi nanoalloys are well distributed on a Vulcan carbon support by a facile, low-cost synthetic strategy. The electrochemical activity of the as-prepared homogeneous PdxBi nanoalloy/carbon black nanocomposites is closely related to the content of Bi, revealing their excellent electrocatalytic performance for selective oxidation of monohydric alcohols and vicinal diols in alkali medium.

Bimetallic Pd96Fe4 nanodendrites embedded in graphitic carbon nanosheets as highly efficient anode electrocatalysts

A facile route to anchor a nanoalloy catalyst on graphitic carbon nanosheets (GCNs) has been developed for preparing high-performance electrode materials for application in direct alcohol fuel cells (DAFCs). Uniformly dispersed bimetallic Pd-Fe nanoparticles (NPs) with tunable composition have been immobilized on GCNs derived from mesocarbon microbeads (MCMBs) by a one-pot radiolytic reduction method. The Pd-Fe/GCN hybrid shows promising electrocatalytic activity for the methanol, ethanol, ethylene glycol, tri-ethylene glycol and glycerol oxidation reactions in alkaline medium. The as-prepared flower-shape Pd₉₆Fe₄/GCN nanohybrids have high mass activity for the ethanol oxidation reaction (EOR), which is ∼36 times (11 A per mg Pd) higher than that of their monometallic counterparts. Moreover, the onset oxidation potential for the EOR on the Pd₉₆Fe₄/GCN nanohybrids negatively shifts ca. 780 mV compared to that on commercial Pd/C electrocatalysts, suggesting fast kinetics and superior electrocatalytic activity. Additionally, chronoamperometry measurements display good long-term cycling stability of the Pd₉₆Fe₄/GCN nanohybrids for the EOR and also demonstrate only ∼7% loss in forward current density after 1000 cycles. The superior catalytic activity and stability may have originated from the modified electronic structure of the Pd-Fe nanoalloys and excellent physicochemical properties of the graphitic nanosheets. The present synthetic route using GCNs as the supporting material will contribute to further design of multimetallic nanoarchitectures with controlled composition and desired functions for fuel cell applications.

Operando Raman probing of electrocatalytic biomass oxidation on gold nanoparticle surfaces

Electrocatalytic conversion of biomass-derived intermediates is a green route to value-added chemicals. However, this technology is just emerging and the mechanisms of this process are not fully resolved. Here, we present the first operando Raman spectroscopic investigation of 5-hydroxymethylfurfural oxidation on gold nanoparticle surfaces, opening up avenues for understanding such reactivity and for rational systems design.