Valorization of Glycerol Through 2,2,6,6‐Tetramethyl‐1‐Piperidine‐N‐Oxyl (TEMPO)‐Catalyzed Electrochemical Oxidation with High C3 Product Selectivity: Impact of Stirred Bulk Versus Flow Electrolysis

Introduction Recently, biodiesel fuel (BDF) attracts attention due to the progress of global warming. Glycerol as a byproduct is produced with BDF, and practically used for pharmaceuticals, cosmetics, food additives and so on. With the mass production of BDF, new applications of the glycerol byproduct need to be found. The application of glycerol as anode for direct alcohol fuel cells (DAFCs) can be an important solution because it has low toxicity and high specific energy (5.0 kWh kg-1). However, glycerol has two C-C bonds and three OH groups, so the mechanism for glycerol oxidation reaction (GOR) is complex,1 and the rate for GOR is so slow that the complete oxidation to CO2 is very difficult. Palladium is known to be one of active materials for GOR. We have found the alloy nanoparticles of Pd with Ag or Au improved the GOR activity and tolerance to the poisoning species on Pd nanoparticle in alkaline medium due to the electronic and bi-functional effects.2 Meanwhile, the Pt electrode had higher GOR activity than the Pd electrode in terms of the onset potential of GOR current, and Ag would improve the GOR activity of Pt. In this study, the effect of the modification with Ag on the GOR activity of a Pt substrate was evaluated by cyclic voltammetry (CV). Moreover, the mechanism for GOR on the Ag-modified Pt (Ag/Pt) electrode was discussed based on in situ infrared reflection absorption spectra at different potentials. Experimental The Ag/Pt electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pt substrate were calculated from the charge for H desorption before and after the Ag modification. The Ag/Pt electrodes with θ Ag = 0.8 and 0.5 were used in this study, which are denoted as Ag(0.8)/Pt and Ag(0.5)/Pt, respectively. The electrolytes were 1 M KOH or (1 M KOH + 0.5 M glycerol) solutions. Pt plate (1 cm × 1 cm) and a Hg/HgO electrode were used as counter and reference electrodes, respectively. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The GOR activity for the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline medium was evaluated by CV (Fig. 1). Both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes had twice higher current density and about 150 mV lower onset potential than the Pt substrate. This means that the enhancement of the GOR activity is caused by the modification of Ag atomic layers. Moreover, as θ Ag increased, a GOR wave was separated into two. The durability for GOR was evaluated by potentiostatic electrolysis for 60 min at -0.1 V and -0.3 V (vs. Hg/HgO). At -0.1 V, the durability for GOR was decreased in the order of Ag(0.5)/Pt > Pt > Ag(0.8)/Pt. On the other hand, at -0.3 V, the Ag(0.5)/Pt electrode still showed the best tolerance to the poisoning species, but the durability for GOR of Ag(0.5)/Pt was poorer than that of Pt. These results indicated that the modification of Ag on Pt improved the GOR activity and durability. IRAS gives us the information on the GOR mechanism. In the case of the Pt electrode, the mainly absorption band are observed at 1310 cm-1, 1335 cm-1, 1350 cm-1, 1385 cm-1 and 1575 cm-1 which can be attributed to glyceraldehyde or glycerate, dihydroxyacetone, hydroxypyruvate, symmetric and symmetric O-C-O stretching of carboxylate, respectively. At higher potentials, the absorption band at 1310 cm-1 was obviously observed. On the other hand, in the case of both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes, the absorption band at 1335 cm-1 due to dihydroxyacetone was more obviously observed at -0.4 to -0.2 V, whereas at -0.2 to 0.1 V, the absorption band at 1310 and 1350 cm-1 was strengthen. This results indicate that the oxidation of primary and secondary OH groups depends on potential, and the secondary OH (-0.4 to -0.2 V) and the primary OH ( -0.1 V) are preferentially oxidized on the Ag modified Pt electrodes. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. References 1) M. Simoes et al., Appl. Catal. B: Environ., 93, 354 (2010).2) B. T. X. Lam et al., J. Power Sources, 297, 149 (2015). Figure 1

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.

Introduction Biodiesel fuel (BDF) attracts attention as a carbon-neutral fuel as well as bioethanol. As the production of BDF increases, the production of the glycerol byproduct is also increasing. It is important to develop new uses for glycerol to cope with the mass production of BDF. The use of glycerol as a fuel for direct alcohol fuel cells is promising, because anodic oxidation of glycerol produced by bioprocesses occurs in carbon-neutral cycles and direct glycerol fuel cells are expected to produce electricity with a low environmental load and to be energy efficient. It is well-known that Pd is cheaper than Pt and Au, and Pd-based alloy electrodes are highly active for the oxidation of alcohols in alkaline media. We also have reported the PdAg alloys-loaded carbon exhibited higher glycerol oxidation reaction (GOR) activity and tolerance to poisoning species than Pd.1 The mechanism for GOR, however, is not so clear. In this study we prepared an Ag atomic layer-modified Pd model electrode, and investigated the potential dependence of GOR products by in situ infrared reflectance-absorption spectroscopy (IRAS). In addition, we discussed the GOR mechanism based on these data. Experimental The Ag atomic layer-loaded Pd (Ag/Pd) electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt polycrystalline substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pd substrate was evaluated to be 0.5 from the charges for Cu-upd before and after the Ag modification. 1 M KOH and (1 M KOH + 0.5 M glycerol) solution were used for electrochemical measurements. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pd and Ag/Pd electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The cyclic voltammograms of the Pd and Ag/Pd electrodes in a (1 M KOH + 0.5 M glycerol) solution is shown in Fig. 1. The Ag/Pd electrode had higher oxidation current and more negative onset potential of the oxidation current than the Pd electrode, clearly indicating that the GOR activity was enhanced by the modification of the Ag atomic layer. In addition, the peak potential of the oxidation current for the Ag/Pd electrode was more positive than that for the Pd electrode, suggesting that the former was superior in tolerance to poisoning species to the latter. IRAS spectra for the Pt electrode exhibited that the absorption peak at 1335 cm-1 assigned to the formation of dihydroxyacetone was mainly increased at lower potentials, but the absorption peak at 1310 cm-1 assigned to the formation of glycerate was increased at higher potentials. This suggests that the secondary OH group in a glycerol molecule is preferentially oxidized at smaller overpotentials, and the primary OH group is greatly oxidized at larger overpotentials. For the Ag/Pd electrode, the oxidation of the primary OH group occurred even at smaller overpotentials, and hydroxypyruvate was also formed at larger overpotentials. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. Reference 1 B. T. X. Lam, M. Chiku, E. Higuchi, H. Inoue, J. Power Sources, 297, 149 (2015). Figure 1

Hydrogen (H2) has been spotlighted as ideal energy carrier due to its relatively higher energy density compared to fossil fuel and no carbon emissions during the energy generation. However, most of current produced H2 comes from as byproducts in fossil fuel reforming processes. To reduce dependence on fossil fuel in the H2 production process, photoelectrochemical (PEC) water splitting is considered as promising strategy for producing H2 using sustainable resources. Nevertheless, the insufficient efficiency in PEC water oxidation oxygen evolution reaction (OER) has limited overall PEC water splitting system efficiency due to its relatively high oxidation potential and sluggish catalytic kinetics. Furthermore, the low value of generated oxygen has been pointed out as obstacle from an economic perspective. To overcome these challenges, glycerol, byproduct of biodiesel, has been attracted numerous attentions as PEC oxidation resource since it has three hydroxyl groups and relatively lower oxidation potential than OER. Furthermore, glycerol oxygenated value-added products like dihydroxyacetone (DHA) can improve economics of PEC hydrogen production system. Upon these strengths, PEC glycerol oxidation reaction (GOR) provides improved strategy that generates value-added products in anodic part and green energy source (H2) in cathodic part simultaneously, which can replace PEC water splitting. Bismuth vanadate (BiVO4) is one of the most promising transition metal oxide based catalyst for PEC GOR due to its relatively narrow bandgap, high theoretical photocurrent density and deep positive valence band maximum (VBM) position. Additionally, although the surface kinetics of BiVO4 for OER has been sluggish, it potentially would be advantage for GOR with high production rate. However, the relatively instability of BiVO4 in acidic electrolyte during operation and lower selectivity of oxygenated products has hindered their practical application in PEC GOR. To solve these problems, introduction of nanoparticles as cocatalysts has been much studied for ameliorating surface kinetics and passivation the surface of photoanode. However, the interface between nanoparticles and photoanode with poor chemical interaction can induce the higher interfacial resistance and slow charge transfer efficiency rather. In this study, we present in-situ vanadium oxide (VOx) nanoparticle decoration on the surface of BiVO4 (VOx/BiVO4) via selective etching process using alkaline treatment for enhancing PEC GOR and we report the world best photocurrent density based on BiVO4 photoanode for GOR with high selective DHA production. VOx nanoparticles with an average size of 5 nm by selective etching process using alkaline treatment is decorated on the surface of BiVO4. The VOx promotes the surface reaction kinetics via modulating the fermi level and enhanced photovoltage of BiVO4 and improves long-term stability for GOR by compensation of V5+ and Bi3+, which combines both efficiency and stability. Furthermore, the surface decorated photoanode presents a 6.82 mA/cm2 (1.34-fold improvement) photocurrent density at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun illumination, which has been attributed enhanced catalytic kinetics with upshifted fermi level and photovoltage of BiVO4. Moreover, the long-term stability of VOx/BiVO4 has been exhibited over 10 hours and the high selectivity for DHA is achieved. This study presents insight into the role vanadium of selective etched VOx on the surface of BiVO4 with low valence state than that of BiVO4 and improving the potential of BiVO4 based catalyst as GOR photoanode for high selective value-added DHA production using solar energy.

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.

The valorisation of glycerol using renewable electricity is recognised as an effective and attractive approach for producing high-value compounds from biomass byproducts. 2D conjugated metal-organic frameworks (2D c-MOFs) have emerged as promising electrocatalysts due to their tunable structures, high electronic conductivity, and efficient utilisation of well-defined active centres. In this study, we report the first systematic investigation of 2D c-MOFs containing Ni-X4 (X=O or N) moieties for the glycerol oxidation reaction (GOR), examining key factors influencing both electrocatalytic activity and selectivity. In situ 13C electrochemical nuclear magnetic resonance and Raman spectroscopies provide insights into the GOR mechanism and confirm that Ni-O4 sites are the primary active centres. Theoretical calculations further reveal that [Ni3(HHTQ)2]n (HHTQ = 2,3,7,8,12,13-hexahydroxytricycloquinazoline) exhibits superior GOR activity due to strong adsorption of reaction intermediates and weak interlayer interactions. This work highlights the potential of 2D c-MOFs as highly efficient GOR catalysts, paving the way for the rational design of advanced electrocatalysts and contributing to the development of sustainable energy conversion and storage technologies.

The valorisation of glycerol using renewable electricity is recognised as an effective and attractive approach for producing high‐value compounds from biomass byproducts. 2D conjugated metal–organic frameworks (2D c‐MOFs) have emerged as promising electrocatalysts due to their tunable structures, high electronic conductivity, and efficient utilisation of well‐defined active centres. In this study, we report the first systematic investigation of 2D c‐MOFs containing Ni‐X4 (X = O or N) moieties for the glycerol oxidation reaction (GOR), examining key factors influencing both electrocatalytic activity and selectivity. In situ 13C electrochemical nuclear magnetic resonance and Raman spectroscopies provide insights into the GOR mechanism and confirm that Ni–O4 sites are the primary active centres. Theoretical calculations further reveal that [Ni3(HHTQ)2]n (HHTQ = 2,3,7,8,12,13‐hexahydroxytricycloquinazoline) exhibits superior GOR activity due to strong adsorption of reaction intermediates and weak interlayer interactions. This work highlights the potential of 2D c‐MOFs as highly efficient GOR catalysts, paving the way for the rational design of advanced electrocatalysts and contributing to the development of sustainable energy conversion and storage technologies.

The transition away from fossil fuels is a global priority due to their limited availability and significant role in CO₂ emissions and climate change. Among sustainable energy solutions, hydrogen (H₂) emerges as a compelling alternative with high energy density and a carbon-neutral profile, making it a strong candidate to replace conventional fossil fuels. However, traditional hydrogen production methods, like steam methane reforming and coal gasification, are inefficient, and produce between 6–10 tonnes of CO2 per each tonne of H2, underscoring the need for greener alternatives, such as water electrolysis. (1) While water electrolysis can be a scalable and sustainable pathway to decarbonize hydrogen production, its adoption is hindered by the high energy demands of the oxygen evolution reaction (OER), which consumes a substantial share of the energy input. Moreover, OER catalysts rely on scarce and costly precious metals like iridium and ruthenium, operating at high voltages under harsh conditions, thereby escalating costs and durability challenges that form critical bottlenecks to industrial scalability.To address the challenges associated with traditional water electrolysis, one promising approach is to explore alternative anodic reactions to replace OER, with the glycerol oxidation reaction (GOR) emerging as a particularly viable candidate. GOR has a low thermodynamic reversible potential requirement of 0.08 V versus the standard hydrogen electrode (SHE) for oxidation to glyceric acid, nearly 1 V lower than water oxidation (1.23 V vs. SHE). Therefore, replacing OER with GOR can reduce the operating voltage of membrane electrode assemblies for hydrogen production. (2) Furthermore, glycerol is an abundant and inexpensive by-product of the biodiesel and soap industries, priced at approximately $0.07/g in 2024 (pure glycerol, 99%), and its electrochemical oxidation can produce high-value chemicals like lactic acid or glyceric acid, commanding market prices of up to $1215/g. (3)However, scaling GOR-integrated systems for industrial applications presents significant challenges, including the development of cost-effective and selective catalysts capable of efficient operation under practical conditions, optimizing reaction parameters to maximize yield and product selectivity, and ensuring long-term operational stability in industrial-scale systems. Catalyst/electrode development is particularly demanding due to challenges like poisoning, limited selectivity for desired products, and deactivation, all of which must be addressed to unlock the full potential of GOR in advancing green hydrogen production. (4)In this study, we present a proof-of-concept demonstration for a GOR-integrated membrane electrode assembly, achieving current densities exceeding 400 mA/cm² at an applied voltage <1.5 V. The catalysts demonstrate over 70% selectivity for high-value C₃ products, including lactic acid, glyceric acid, and tartronic acid. These findings highlight the transformative potential of GOR integration as a viable alternative to the OER, paving the way for more efficient, economically attractive, and sustainable hydrogen production technologies. References Chauhan I, Bajpai H, Ray B, Kolekar SK, Datar S, Patra KK, et al. Electrocatalytic Glycerol Conversion: A Low-Voltage Pathway to Efficient Carbon-Negative Green Hydrogen and Value-Added Chemical Production. ACS Applied Materials & Interfaces. 2024;16(20):26130-41.Ebeling KM, Bongartz D, Mürtz S, Palkovits R, Mitsos A. Thermodynamic and Economic Potential of Glycerol Oxidation to Replace Oxygen Evolution in Water Electrolysis. Industrial & Engineering Chemistry Research. 2024;63(18):8250-60.Angizi S, Nankali M, Foroozan A, Park J, Yelekli Kirici E, Noor N, et al. 3D Bimetallic Platinum-Nickel Electrodes for Electro-Oxidation of Glycerol at Ambient Conditions. Advanced Functional Materials.n/a(n/a):2420622.Angizi S, Kirici EY, Higgins D. Toward valorization of crude glycerol via controlled electro-oxidation. Trends in Chemistry. 2024;6(1):14-21.

Over the last years, biodiesel production, a renewable fuel derived from biomass, has significantly increased, reaching an output of 40 million tons annually. This surge in production has resulted in excessive glycerol production, as a byproduct, accounting for 10 wt.% of biodiesel production. By 2025, it is predicted that glycerol production will amount to 6.3 million tons.1 However, the low demand for glycerol not only causes high disposal costs for this waste byproduct but also poses a threat to the ecosystem. Consequently, the valorization of glycerol is crucial for enhancing the biodiesel industry's economic viability and environmental sustainability.Among all the techniques for the valorization of glycerol, such as catalytic oxidation, dehydration, and hydrogenolysis, the electrochemical oxidation of glycerol stands out for its cost-effectiveness, simplicity, and eco-friendliness. The glycerol electrooxidation reaction (GOR) can yield a wide range of valuable chemicals, such as C3 products (glyceraldehyde, lactic acid, glyceric acid, tartronic acid), C2 products (glycolic acid, oxalic acid, acetic acid), and C1 products (formic acid). Among all the products, C3 products have notably higher economic value compared to others. In particular, glyceric acid stood out by having a price of over 200 folds of glycerol and having the highest worldwide demand among all the GOR products.2 However, a significant technical challenge lies in developing a highly selective catalyst for C3 products showing high activity, and stability. Thus far, most of the catalyst developed for GOR includes noble metals or their alloys, which limits their usage in realistic systems due to their high cost and scarcity.3 Therefore, developing a cost-effective catalyst with high selectivity, activity, and stability is necessary to make the valorization of glycerol economically viable.In this work, we demonstrate a bimetallic catalyst that, despite its low noble metal content, achieves high selectivity towards glyceric acid, along with notable catalytic activity and stability. Our analysis focuses on the impact of noble metal amount on activity and stability, and parametric analysis to improve the selectivity of C3 products. Furthermore, we outline the reasons for the discrepancies in the quantification of GOR products, especially in applying H-NMR analysis, and discuss the methods to improve the precision in GOR product analysis.

ABSTRACTThe electrocatalytic glycerol oxidation reaction (GOR) offers a promising route to synthesize high value-added chemicals, for example glyceric acid (GLA), in an economic and sustainable manner. Despite some great achievements, GLA selectivity and yield rate of GOR electrocatalysis remain unsatisfactory due to uncontrollable C–C bond cleavage of glycerol (for unfavorable C1 and C2 products). In this work, rare-earth-metal (REM)-alloyed PtPb mesoporous nanosheets are demonstrated as novel yet high-performance electrocatalysts for selective GLA electrosynthesis from GOR. The best electrocatalyst—PtPbY MNSs—delivers outstanding performance for GLA electrosynthesis from glycerol, including superior selectivity of 72.5% and recordable yield rate of 656 μmol mgcat−1 h−1, surpassing most electrocatalysts reported in the literature. Meanwhile, PtPbY MNSs hold impressive stability of GOR electrocatalysis, retaining the high GLA selectivity and yield rate for reaching 15 cycles. Superior performance, revealed by in situ characterizations and density functional theory calculations, is ascribed to structural and compositional synergies that kinetically promote the reactivity of glycerol and accelerate the desorption of GLA while minimizing undesirable C–C bond cleavage. This work elaborates a powerful alternative for selective electrosynthesis of high-value-added chemicals from waste alcohols by optimizing chemisorption properties of mesoporous metals by REM alloys.

Glycerol, as the primary by‐product in the biodiesel production process, is abundant and cost‐effective. Its efficient conversion into other chemicals offers a promising strategy for alleviating the energy crisis. Electrocatalytic glycerol oxidation reaction (GOR) holds significant application potential due to its mild reaction conditions and lack of additional oxidants, enabling the production of various value‐added chemicals such as lactic acid (LA), dihydroxyacetone (DHA), glyceric acid (GLA), oxalic acid (OA), and formic acid (FA). When GOR is used to replace the oxygen evolution reaction (OER), it enables the coproduction of high‐value oxidation products and H 2 while minimizing energy consumption and carbon dioxide emissions. This has important research significance and value for the conversion of biomass resources and the energy‐efficient production of “green hydrogen.” Consequently, designing efficient and low‐cost electrocatalysts to achieve high activity and selectivity in GOR is a central research objective. Among these, transition metal materials demonstrate significant advantages. This review introduces the types of transition metal catalysts used for GOR and discusses recent catalyst design strategies to enhance GOR activity and selectivity, including nanostructure regulation, defects and surface engineering, heterostructure construction, and single‐atom catalysts. In addition, the practical applications of GOR as well as sustainability studies are discussed. Finally, we summarize the current challenges facing transition metal catalysts in GOR and discuss future prospects.

Coupling nitrate reduction reaction (NO3RR) with glycerol oxidation reaction (GOR) establishes a sustainable "C─N co-conversion" electrolysis system to generate ammonium formate. Unfortunately, the rational design of high-performance bifunctional electrocatalysts remains challenging. Herein, we developed a 3D Ag/Ru-decorated CuO/Cu(OH)2 heterostructures supported by copper foams via interface engineering. The optimal catalyst exhibited outstanding NO3RR and GOR performance, achieving Faradaic efficiency (FE) of 97.3% and yield of 9.85 mg h-1 cm-2 at -0.5 V vs. RHE for NH3 synthesis, and FE of 82.6% and yield of 90.31 mg h-1 cm-2 at 1.55 V vs. RHE for formate production. Mechanistic studies revealed that the decoration of Ag and Ru atoms led to electron redistribution around the copper sites, promoting proton-coupled electron transfer and optimizing the adsorption of the reactants/intermediates. Notably, on the basis of the as-prepared bifunctional electrode, a "NO3RR || GOR" electrolyzer was constructed, which achieved simultaneous output of NH3 and formate with a current density of 100 mA cm-2 at only 1.48 V. The performance of the electrolyzer was further demonstrated using simulated nitrate pollutants and crude glycerol as feedstock, yielding 20.9 g of ammonium formate via a 4-h electrolysis. This work demonstrates a sustainable pathway for the synthesis of high-value-added ammonium formate by constructing an efficient bifunctional electrocatalyst through rational interfacial engineering.

Electrochemical glycerol oxidation reaction (GOR) is an attractive alternative anodic reaction to oxygen evolution reaction for a variety of electrolytic synthesis, thanks to the possibility of mass production of glycerol from biomass and the relative low thermodynamic potential of GOR. The development of high-activity cheap electrocatalysts toward GOR yet faces a daunting challenge. Herein, we experimentally prepare a new range of high entropy alloy (HEA) self-supported electrodes with uniform HEA nanoparticles grown on carbon cloth. The systematic electrochemical studies verify that the HEA-CoNiCuMnMo electrode exhibits attractive performance for GOR electrocatalysis with low overpotential and high selectivity toward formate products. The surface atomic configurations of HEA-CoNiCuMnMo are studied by a self-developed machine learning-based Monte Carlo simulation, which points out the catalytic active center to be Mo sites coordinated by Mn, Mo, and Ni. We further develop a hybrid alkali/acid flow electrolytic cell by pairing alkaline GOR with acidic hydrogen evolution reaction using the HEA-CoNiCuMnMo and the commercial RhIr/Ti as the anode and the cathode, respectively, which only requires an applied voltage of 0.55 V to reach an electrolytic current density of 10 mA cm-2 and maintains long-term electrolysis stability over 12 days continuous running at 50 mA cm-2 with Faraday efficiencies of over 99% for H2 in the cathode and 92% for formate production in the anode.

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.

The glycerol oxidation reaction (GOR) has high potential in substituting the oxygen evolution reaction (OER) in electrochemical water splitting, enabling the synthesis of value‐added organic products. The Cu‐rich Cu−Co hydroxycarbonates show high activity in GOR and promote formate production but undergo severe Cu leaching in the presence of deprotonated glycerol. In this work, the electrooxidation of solketal (SOR), acetal‐protected glycerol, is explored over a series of Cu−Co hydroxycarbonates, to promote the formation of glycerol‐derived C3 products, such as glyceric acid, with faradaic efficiencies of around 70 %, and to limit the Cu leaching from the catalyst. The competition between OER and SOR was evaluated using rotating disk electrodes and differential electrochemical mass spectrometry. Insights into the solketal de‐acetalization as a function of potential are obtained using in situ spectroscopic methods. The solketal/OH− ratio influences the reaction selectivity, with oxalate production increasing when 7 m KOH is used instead of 1 m KOH.