Modification of Nickel Surfaces by Bismuth: Effect on Electrochemical Activity and Selectivity toward Glycerol

Charge Redistribution in Co-Doped Nickel Sulfide to Accelerate Its Alcohol Electrooxidation

Electrochemical alcohol oxidation reaction (AOR) coupled with hydrogen evolution reaction is a significant way to coproduce green hydrogen and value-added chemicals with a low energy consumption. Herein, we report the synthesis of a series of M-doped (M = Co, Fe, and Cu) nickel sulfide nanowires (NWs), and the obtained Ni2Co1S2 NWs exhibit high AOR performance. It shows a high benzyl alcohol oxidation activity of 56.8 mA/cm2 at 1.35 V, which is 24.6 times as high as the activity for Ni3S2 NWs and also better than for most of the reported catalysts. The Ni2Co1S2 NWs also show high activity for glycerol and ethylene glycol oxidations. The high AOR activity of Ni2Co1S2 is attributed to the optimized charge redistribution induced by Co, which promotes the formation of the AOR active Ni(III) species. These results suggest the redistributed charge induced by foreign elements could significantly promote the catalytic performance, and the obtained catalysts are promising for AOR.

Coupling of CuO@NiBiOx Catalyzed Glycerol Oxidation to Carbon Dioxide Reduction Reaction for Enhanced Energy Efficiency

Glycerol electrooxidation reaction (GEOR) is a promising alternative to the oxygen evolution reaction (OER) in electrolyzers, overcoming the inherent challenges of high energy demand and low-value output of water oxidation. Here, we designed a non-noble metal-based electrocatalyst (CuO@NiBiOx, CNBO) for selective and efficient GEOR. The CNBO catalyst demonstrated high selectivity and achieved nearly 100% GEOR Faradaic efficiency (FE), 80%-90% of which is conveyed into formic acid (FA). Bismuth incorporation modified the structure of the mixed oxide, increasing the surface concentration of Ni(III) species and enhancing the GEOR activity. In situ studies confirmed the formation of NiOOH, which is identified as the active site for GEOR and suggests an indirect GEOR mechanism. This study demonstrates the potential of GEOR to replace OER in Carbon dioxide reduction reaction (CO2RR) electrolyzers. Depending on the selected CO2RR catalyst (Ag or Sn), we could obtain either an easy-to-separate mixture of high-added value products (CO and FA) or a single product (FA) with FEFA > 85% at both electrodes. Moreover, we demonstrate that replacing OER with GEOR in a CO2RR-electrolyzer can save up to 25% of the electrolysis energy input, while the co-production of FA at both electrodes halves the energy per mole required for its electrosynthesis.

Mechanistic Insights into Glycerol Oxidation to High-Value Chemicals via Metal-Based Catalysts

The oxidation of glycerol offers a valuable route for producing high-value chemicals. This review provides an in-depth analysis of the current advancements and mechanistic insights into novel metal-based catalysts for glycerol oxidation. We discuss the catalytic roles of both precious metals (e.g., Pt, Pd, Au), noted for their high efficiency and selectivity, and cost-effective alternatives, such as Ni, Cu, and Fe. Bimetallic and metal oxide catalysts are highlighted, emphasizing synergistic effects that enhance catalytic performance. This review elucidates the key mechanism involving selective adsorption and oxidation, providing detailed insights from advanced spectroscopic and computational studies into the activation of glycerol and stabilization of key intermediates, including glyceraldehyde and dihydroxyacetone. Additionally, selective carbon-carbon bond cleavage to yield smaller, valuable molecules is addressed. Finally, we outline future research directions, emphasizing the development of innovative catalysts, deeper mechanistic understanding, and sustainable process scale-up, ultimately advancing efficient, selective, and environmentally friendly catalytic systems for glycerol valorization.

Delineating Catalyst Deactivation Mechanisms in Electrocatalytic Glycerol Oxidation toward Biodiesel Wastewater/CO2 Co-valorization

Biodiesel plays a key role in achieving economy-wide decarbonization but its production discharges significant amounts of CO2 and glycerol-laden wastewater. Given the increasing abundance of biodiesel wastewater and low redox potential of glycerol, coupling the glycerol oxidation reaction (GOR) with CO2 electrolysis has emerged as an attractive strategy to achieve sustainable wastewater management, CO2 utilization, and green chemical synthesis in a single unit process. Despite the need for highly stable catalysts, few studies have examined electrocatalyst deactivation in environmental waste streams. Here, we present a first-of-a-kind diagnostic study that investigates nickel (Ni) catalyst stability during the GOR in synthetic biodiesel wastewaters. A current decline of 99.7% was observed within 24 h of operation. This coincided with an 80% decrease in surface active Ni(II)/Ni(III) concentrations, 190-fold increases in interfacial impedance, and the appearance of electrode C-bonds that suggested surface coverage by GOR reactants and intermediates was likely a main contributor to loss in catalytic activity. Analyses in more complex electrolytes containing methanol and oleate suggested the emergence of distinct deactivation mechanisms through restricted NiOOH formation. Altogether, this study details several previously unreported catalyst deactivation mechanisms. These findings can ultimately help inform future catalyst design toward more practical and sustainable waste valorization.

Ordered Pt3Mn Intermetallic Setting the Maximum Threshold Activity of Disordered Variants for Glycerol Electrolysis

Glycerol electrolysis is a promising strategy for generating hydrogen at the cathode and value-added products at the anode. However, the effect of the atomic distribution within catalysts on their catalytic performance remains largely unexplored, primarily because of the inherent complexity of the glycerol oxidation reaction (GOR). Herein, an ordered Pt3Mn (O-Pt3Mn) intermetallic compound and a disordered Pt3Mn (D-Pt3Mn) alloy are used as model catalysts, and their performance in the GOR and hydrogen evolution reaction (HER) is studied. O-Pt3Mn consistently outperforms D-Pt3Mn and commercial Pt/C catalysts. It can generate high-value glycerate at a notable production rate of 17 mM h-1 while achieving an impressively low cell voltage of 0.76 V for glycerol electrolysis, which is ∼0.98 V lower than that required for water electrolysis. Statistical analysis using theoretical calculations reveals that Pt-Pt-Pt hollow sites are crucial for the catalytic GOR and HER. The averaged adsorption energies of key intermediates (simplified as C*, O*, and H*) on diverse catalysts closely correlate with their experimentally observed activity. Our proposed linear models accurately predict these adsorption energies, exhibiting high correlation coefficients ranging from 0.97 to 0.99 and highlighting the significance of the distribution of the topmost and subsurface-corner Mn atoms in determining these adsorption energies. By sampling all possible Mn configurations within the fitted linear models, we confirm that O-Pt3Mn establishes the maximum activity threshold for the GOR and HER compared with any disordered variant. This study presents an innovative framework for exploring the effect of the atomic distribution within catalysts on their catalytic performance and designing high-performance catalysts for complex reactions.

Galvanostatic Electroshock Synthesis of Low Loading Au-Pt Nanoalloys Onto Gas Diffusion Electrodes as Multifunctional Electrocatalysts for a Glycerol-Fed Electrolyzer

Water electrolysis is increasingly considered a viable solution for meeting the world's growing energy demands and mitigating environmental issues. An inventive strategy to mitigate the energy requirements involves substituting the energy-intensive oxygen evolution reaction (OER) with biomass-derived glycerol electrooxidation. Nonetheless, the synthesis of electrocatalysts for controlling the selectivity towards added-value chemicals at the anode and efficient H2 generation at the cathode remains a critical bottleneck. Herein, we implemented a galvanostatic electroshock synthesis approach to control the reduction kinetics of Au(III) and Pt(IV) to grow ultra-low amount of gold-platinum alloys on a gas diffusion electrode (12-26 μgmetal cm-2) for glycerol-fed hydroxide anion exchange membrane based electrolyzer. The symmetric GDE-Au100-xPtx||GDE-Au100-xPtx systems showed a notable improvement in electrolyzer performance (GDE-Au64Pt36=201 mA cm-2) as compared to monometallic versions (GDE-Au100Pt0=18 mA cm-2, GDE-Au0Pt100=81 mA cm-2). Chromatography (HPLC) analysis underscores the critical importance of bulk electrolysis methodology (galvanostatic vs potentiostatic) for the efficient conversion of glycerol into high-value-added products. Regarding the electrical energy required to produce 1 kg of H2 for such an electrolyzer fed at the anode with glycerol, our results confirm a drastic decrease by a factor of at least two compared with conventional water electrolysis.

Electrochemical and Non-Electrochemical Pathways in the Electrocatalytic Oxidation of Monosaccharides and Related Sugar Alcohols into Valuable Products

In this contribution, we review the electrochemical upgrading of saccharides (e.g., glucose) and sugar alcohols (e.g., glycerol) on metal and metal-oxide electrodes by drawing conclusions on common trends and differences between these two important classes of biobased compounds. For this purpose, we critically review the literature on the electrocatalytic oxidation of saccharides and sugar alcohols, seeking trends in the effect of reaction conditions and electrocatalyst design on the selectivity for the oxidation of specific functional groups toward value-added compounds. Importantly, we highlight and discuss the competition between electrochemical and non-electrochemical pathways. This is a crucial and yet often neglected aspect that should be taken into account and optimized for achieving the efficient electrocatalytic conversion of monosaccharides and related sugar alcohols into valuable products, which is a target of growing interest in the context of the electrification of the chemical industry combined with the utilization of renewable feedstock.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Lignocellulosic materials extraction from waste baby diaper to prepare light-responsive metal oxide/carbon composite for efficient organic dye pollutant removal

The bimetal oxide comprising nickel incorporated β-Bi2O3 on graphitic carbon in the form of bismuth nickel oxide (BNO@C) was prepared by waste lignocellulosic materials collected from cheap and readily available baby diapers. The prepared BNO@C was used to photocatalytically degrade methylene blue under UV-light irradiation. Prior to the photocatalytic performance analysis, the formation of BNO@C was confirmed by various morphological and structural analysis including SEM, TEM, XRD, and XPS analyses. As a result, the two-dimensional nanosheet morphology and tetragonal primitive lattice-structure with 2+ and 3+ oxidation stated Ni and Bi in BNO@C structural formulation were confirmed. In photocatalysis experimentation examined with BNO@C, the maximum methylene blue removal percentage of 96.7 % was achieved within 16 min. The influence of Ni2+ in BNO@C was identified by performing the photocatalytic performance of bare NiO@C and Bi2O3@C, yielding maximum dye removal of 32.8 % and 64.5 %, respectively. The efficacy of Ni in BNO@C toward increasing catalytic efficiency was identified using DFT analysis, revealing the acting of Ni as active sites for improved light absorption tendency. These findings show a novel strategy to prepare a low-cost BNO@C catalyst with efficient photocatalytic activity, opening a new path for a cost-efficient wastewater treatment approach.

Electrocatalytic Glycerol Upgrading into Glyceric Acid on Ni3Sn Intermetallic Compound

Electrochemical glycerol oxidation features an attractive approach of converting bulk chemicals into high-value products such as glyceric acid. Nonetheless, to date, the major product selectivity has mostly been limited as low-value C1 products such as formate, CO, and CO2, due to the fast cleavage of carbon-carbon (C-C) bonds during electro-oxidation. Herein, the study develops an atomically ordered Ni3Sn intermetallic compound catalyst, in which Sn atoms with low carbon-binding and high oxygen-binding capability allow to tune the adsorption of glycerol oxidation intermediates from multi-valent carbon binding to mono-valent carbon binding, as well as enhance *OH binding and subsequent nucleophilic attack. The Ni3Sn electrocatalyst exhibits one of the highest glycerol-to-glyceric acid performances, including a high glycerol conversion rate (1199 µmol h-1) and glyceric acid selectivity (62 ± 3%), a long electrochemical stability of > 150 h, and the capability of direct conversion of crude glycerol (85% purity) into glyceric acid. The work features the rational design of highly ordered catalytic sites for tailoring intermediate binding and reaction pathways, thereby facilitating the efficient production of high-value chemical products.

Regulation of the d-band center of metal-organic frameworks for energy-saving hydrogen generation coupled with selective glycerol oxidation

The hybrid electrolyzer coupled glycerol oxidation (GOR) with hydrogen evolution reaction (HER) is fascinating to simultaneously generate H2 and high value-added chemicals with low energy input, yet facing a challenge. Herein, Cu-based metal-organic frameworks (Cu-MOFs) are reported as model catalysts for both HER and GOR through doping of atomically dispersed precious and nonprecious metals. Remarkably, the HER activity of Ru-doped Cu-MOF outperformed a Pt/C catalyst, with its Faradaic efficiency for formate formation at 90% at a low potential of 1.40 V. Furthermore, the hybrid electrolyzer only needed 1.36 V to achieve 10 mA cm-2, 340 mV lower than that for splitting pure water. Theoretical calculations demonstrated that electronic interactions between the host and guest (doped) metals shifted downward the d-band centers (εd) of MOFs. This consequently lowered water adsorption and dissociation energy barriers and optimized hydrogen adsorption energy, leading to significantly enhanced HER activities. Meanwhile, the downshift of εd centers reduced energy barriers for rate-limiting step and the formation energy of OH*, synergistically enhancing the activity of MOFs for GOR. These findings offered an effective means for simultaneous productions of hydrogen fuel and high value-added chemicals using one hybrid electrolyzer with low energy input.

Enhancing the performance of Ni nanoparticle modified carbon felt towards glycerol electrooxidation: impact of organic additive

Organic additives are widely used in the deposition baths of metals and alloys thanks to their special function which affects the growth and the building of the crystal. This study investigates the effect of glycerol on Ni deposition onto carbon felt (CF) and its effect on the catalytic activity towards glycerol electrooxidation. The impact of glycerol on the morphology, distribution, and particle size of the electrodeposited Ni is disclosed using a scanning electron microscope (SEM). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) techniques were used to probe the possible changes of the electrodeposited Ni oxide phases. Electrochemical measurements show that the as-synthesized Ni_0.05@CF electrocatalyst prepared in the presence of 50 mM glycerol has a marked activity towards glycerol electrooxidation, as confirmed by the impressive increase of the oxidation current by about 1.6 times concurrently with a favorable negative shift of its onset potential. Moreover, the charge transfer resistance (R _ct) is much reduced from 140 to 87 ohm. The addition of glycerol to the deposition bath is believed to retard the growth of the formed Ni deposits while enhancing the nucleation rate and thus increases the particle density and, consequently, the distribution of deposited Ni over the entire CF is improved along with increasing the surface concentration and surface-active sites. This assumption is supported by density functional theory (DFT) calculations.

Ligand Hybridization for Electro-reforming Waste Glycerol into Isolable Oxalate and Hydrogen

The electro-reforming of glycerol is an emerging technology of simultaneous hydrogen production and biomass valorization. However, its complex reaction network and limited catalyst tunability restrict the precise steering toward high selectivity. Herein, we incorporated the chelating phenanthrolines into the bulk nickel hydroxide and tuned the electronic properties by installing functional groups, yielding tunable selectivity toward formate (max 92.7 %) and oxalate (max 45.3 %) with almost linear correlation with the Hammett parameters. Further combinatory study of intermediate analysis and various spectroscopic techniques revealed the electronic effect of tailoring the valence band that balances between C-C cleavage and oxidation through the key glycolaldehyde intermediate. A two-electrode electro-reforming setup using the 5-nitro-1,10-phenanthroline-nickel hydroxide catalyst was further established to convert crude glycerol into pure H₂ and isolable sodium oxalate with high efficiency.

Tailor-designed binary Ni-Cu nano dendrites decorated 3D-carbon felts for efficient glycerol electrooxidation

Herein, 3D-Carbon Felt (CF) are decorated with nickel-copper (Ni-Cu@CF) bimetallic nanostructures through either sequential or co-electrodeposition tactics. Their catalytic activity towards glycerol electrooxidation is investigated by employing cyclic voltammetry (CV) and linear sweep voltammetry LSV. The morphology and composition of the various Ni-Cu@CF are investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) together with various electrochemical measurements (e.g., CV, chronoamperometry, LSV). The co-deposition of Ni-Cu shows a dendritic-like structure with higher electrocatalytic activity towards glycerol electrooxidation compared to the monometallic counterparts. Interestingly, the best electrode (NiCu@CF Ni particles as the top layer) prepared by sequential electrodeposition shows 1.6-fold higher glycerol oxidation activity, manifested in oxidation current, compared to Ni-coated CF due to Ni particles covering the surface of dendritic copper uniformly. Thus, the surface concentration of Ni is increased and at the same time a synergistic effect occurs between Ni and Cu by the simple addition of Cu which reinforces the surface concentration of Ni from 3.4 × 10-8 to 1.1 × 10-7 mol cm-2.

Predictive control of selective secondary alcohol oxidation of glycerol on NiOOH

Many biomass intermediates are polyols and selectively oxidizing only a primary or secondary alcohol group is beneficial for the valorization of these intermediates. For example, production of 1,3-dihydroxyacetone, a highly valuable oxidation product of glycerol, requires selective secondary alcohol oxidation. However, selective secondary alcohol oxidation is challenging due to its steric disadvantage. This study demonstrates that NiOOH, which oxidizes alcohols via two dehydrogenation mechanisms, hydrogen atom transfer and hydride transfer, can convert glycerol to 1,3-dihydroxyacetone with high selectivity when the conditions are controlled to promote hydrogen atom transfer, favoring secondary alcohol oxidation. This rational production of 1,3-dihydroxyacetone achieved by selectively enabling one desired dehydrogenation pathway, without requiring alteration of catalyst composition, demonstrates how comprehensive mechanistic understanding can enable predictive control over selectivity.

Direct 3D Printing of Binder-Free Bimetallic Nanomaterials as Integrated Electrodes for Glycerol Oxidation with High Selectivity for Valuable C3 Products

Net-zero carbon strategies and green synthesis methodologies are key to realizing the United Nations' sustainable development goals (SDGs) on a global scale. An electrocatalytic glycerol oxidation reaction (GOR) holds the promise of upcycling excess glycerol from biodiesel production directly into precious hydrocarbon commodities that are worth orders of magnitude more than the glycerol feedstock. Despite years of research on the GOR, the synthesis process of nanoscale electrocatalysts still involves (1) prohibitive heat input, (2) expensive vacuum chambers, and (3) emission of toxic liquid pollutants. In this paper, these knowledge gaps are closed via developing a laser-assisted nanomaterial preparation (LANP) process to fabricate bimetallic nanocatalysts (1) at room temperature, (2) under an ambient atmosphere, and (3) without liquid waste emission. Specifically, PdCu nanoparticles with adjustable Pd:Cu content supported on few-layer graphene can be prepared using this one-step LANP method with performance that can rival state-of-the-art GOR catalysts. Beyond exhibiting high GOR activity, the LANP-fabricated PdCu/C nanomaterials with an optimized Pd:Cu ratio further deliver an exclusive product selectivity of up to 99% for partially oxidized C₃ products with value over 280000-folds that of glycerol. Through DFT calculations and in situ XAS experiments, the synergy between Pd and Cu is found to be responsible for the stability under GOR conditions and preference for C₃ products of LANP PdCu. This dry LANP method is envisioned to afford sustainable production of multimetallic nanoparticles in a continuous fashion as efficient electrocatalysts for other redox reactions with intricate proton-coupled electron transfer steps that are central to the widespread deployment of renewable energy schemes and carbon-neutral technologies.

Modulating p-Orbital of Bismuth Nanosheet by Nickel Doping for Electrocatalytic Carbon Dioxide Reduction Reaction

Electrochemical reduction of CO₂ (CO₂ RR) to value-added chemicals is an effective way to harvest renewable energy and utilize carbon dioxide. However, the electrocatalysts for CO₂ RR suffer from insufficient activity and selectivity due to the limitation of CO₂ activation. In this work, a Ni-doped Bi nanosheet (Ni@Bi-NS) electrocatalyst is synthesized for the electrochemical reduction of CO₂ to HCOOH. Physicochemical characterization methods are extensively used to investigate the composition and structure of the materials. Electrochemical results reveal that for the production of HCOOH, the obtained Ni@Bi-NS exhibits an equivalent current density of 51.12 mA cm^-2 at -1.10 V, which is much higher than the pure Bi-NS (18.00 mA cm^-2 at -1.10 V). A high Faradaic efficiency over 92.0 % for HCOOH is achieved in a wide potential range from -0.80 to -1.10 V, and particularly, the highest efficiency of 98.4 % is achieved at -0.90 V. Both experimental and theoretical results reveal that the superior activity and selectivity are attributed to the doping effect of Ni on the Bi nanosheet. The density functional theory calculation reveals that upon doping, the charge is transferred from Ni to the adjacent Bi atoms, which shifts the p-orbital electronic density states towards the Fermi level. The resultant strong orbital hybridization between Bi and the π* orbitals of CO₂ facilitates the formation of *OCHO intermediates and favors its activation. This work provides an effective strategy to develop active and selective electrocatalysts for CO₂ RR by modulating the electronic density state.

Electro-Oxidation of Glycerol to High-Value-Added C1-C3 Products by Iron-Substituted Spinel Zinc Cobalt Oxides

Glycerol is a byproduct of biodiesel production and can be a low-cost source for some high-value C1-C3 chemicals. The conversion can be achieved by photo-, thermo-, and electro-catalysis methods. The electrocatalytic oxidation method is attractive due to its moderate reaction conditions and high electron to product efficiency. Most reported catalysts are based on noble metals, while metal oxides are rarely reported. Here, we investigated the electro-oxidation of glycerol on a series of ZnFe_xCo_2-xO₄ (x = 0, 0.4, 1.0, 1.4, and 2.0) spinel oxides. Seven types of value-added C1-C3 products including formate, glycolate, lactate, and glycerate can be obtained by this approach. The selectivity and Faraday efficiency toward these products can be tuned by adjusting the Fe/Co ratio and other experimental parameters, such as the applied potential, glycerol concentration, and electrolyte pH.