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Article

Enhanced Electrocatalytic Performance for Selective Glycerol Oxidation to Formic Acid at a Multiphase AuCu-Ag/AgBr Interface

by
Jianchuan Jin
,
Luyao Sun
,
Zhiqing Wang
,
Shiyu Li
,
Lingqin Shen
* and
Hengbo Yin
*
School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Rd., Zhenjiang 212013, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(9), 831; https://doi.org/10.3390/catal15090831 (registering DOI)
Submission received: 21 July 2025 / Revised: 21 August 2025 / Accepted: 25 August 2025 / Published: 1 September 2025
(This article belongs to the Special Issue Heterogeneous Catalysts for Biomass Conversions)
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Abstract

Electrochemical glycerol oxidation presents a sustainable and environmentally friendly pathway for formic acid production, addressing the significant carbon emissions and resource dependency associated with conventional industrial processes. However, the development of advanced electrocatalysts with high formic acid selectivity and durability remains challenging due to the polyhydroxy structure and carbon chain complexity of glycerol, which lead to intricate oxidation pathways and a wide variety of products. To tackle this issue, we report a AuCu-Ag/AgBr catalyst with a multiphase interface, referring to the integrated boundaries among AuCu, Ag, and AgBr phases that interact with the liquid electrolyte, for high-rate and high-efficiency glycerol oxidation. Comprehensive characterizations reveal that the multiphase interface may effectively modulate the adsorption configurations of glycerol molecules and enhance charge transfer efficiency. Under ambient conditions, glycerol electro-oxidation at 1.43 V for 8 h yielded a conversion of 38% and a formic acid selectivity of 81%, and recycling tests confirmed its high stability under prolonged electrolysis. This synergistic catalytic effect provides a kinetically favorable pathway for formic acid production, demonstrating the potential of AuCu-Ag/AgBr catalysts in advancing sustainable glycerol valorization.

Graphical Abstract

1. Introduction

In response to escalating global environmental degradation and climatic variations [1], the imperative to harness renewable energy alternatives has become paramount in reducing dependence on traditional fossil-based energy systems [2,3,4,5]. Glycerol, an abundant and low-cost byproduct of biodiesel production [6], has emerged as a promising feedstock for value-added chemical synthesis, particularly within the context of global carbon neutrality strategies [7,8,9,10,11]. However, due to the presence of various impurities, crude glycerol is unsuitable for direct application in the pharmaceutical and food industries [12,13]. Electrochemical oxidation offers an attractive alternative to conventional purification methods by enabling the direct conversion of crude glycerol into a variety of oxygenated products [14]. Due to its multiple hydroxyl functional groups, glycerol can be selectively oxidized to produce C1–C3 oxygenates, including formic acid (C1) [15], glycolic acid, acetic acid, and oxalic acid (C2) [16,17], as well as glyceraldehyde, lactic acid, tartronic acid, dihydroxyacetone, and glyceric acid (C3) [18,19,20]. We acknowledge that many of these products, such as dihydroxyacetone, tartronic acid, and glycolic acid, have high market value and significant industrial applications. In this work, we focused on formic acid primarily because of its high theoretical yield from glycerol (up to 3 mol FA per mol glycerol) and relatively straightforward separation from aqueous reaction mixtures. Additionally, formic acid is an important industrial chemical with growing relevance as a hydrogen carrier and fuel additive [15,21]. Conventional FA production relies on methanol carbonylation under harsh conditions [22], whereas electrocatalytic oxidation of glycerol provides a milder and more sustainable pathway, potentially enabling co-production of clean hydrogen at the cathode [23,24]. Considering these factors, formic acid was selected as the main target product in this study while recognizing that future investigations may explore other high-value oxidation products.
A key challenge in the electrocatalytic oxidation of glycerol to formic acid lies in the development of efficient anodic catalysts that can enhance the Faradaic efficiency for formic acid, by harnessing selective C–C bond cleavage. To date, the use of noble metal-based catalysts, particularly those composed of Au [25], Pd [26], Pt, and their alloys, has been widely explored for the selective electro-oxidation of glycerol under alkaline conditions [27,28]. Among them, gold-based catalysts have shown exceptional activity and selectivity. For instance, Xie et al. reported that a Au/CP catalyst exhibited remarkable performance for glycerol oxidation, achieving 97% selectivity toward glyceric acid at 1.0 V, while shifting to predominant formic acid production at 1.3 V [29]. Similarly, Zhang et al. explored Au catalysts supported on carbon nanotubes and found that higher applied potentials and optimized electrolyte conditions favored glycolic acid formation, with up to 85% selectivity, albeit with limited glycerol conversion (34%) [30]. Gomes et al. investigated the effect of Ag incorporation in AuAg/C catalysts and found that Ag effectively lowered the onset potential for glycerol oxidation, facilitating more efficient C–C bond cleavage [31]. AuAg@TiO2 [32], PtxAuy@Ag [33], and AuAg [34] alloy have also been employed in glycerol oxidation, yielding 1,3-dihydroxyacetone and lactic acid as the main products. Collectively, these studies confirm that Au-based catalysts can effectively mediate both C–C bond cleavage and hydroxyl group oxidation, enabling the formation of a spectrum of C1–C3 carboxylic acids. These findings suggest that rational interfacial engineering of Au-based catalysts can enhance both catalytic efficiency and product selectivity. In particular, bimetallic and interfacial designs that promote favorable electronic and geometric configurations hold promise for directing glycerol oxidation pathways toward desirable C1 products such as formic acid.
Building on these insights, the rational design of multicomponent and heterointerfacial catalysts has emerged as an effective strategy to further modulate the electronic structure and reaction pathways of Au-based systems. In this context, constructing well-defined multiphase interfaces that incorporate Trimetallic components and halide species holds great potential for optimizing activity, selectivity, and stability. Herein, we report a AuCu-Ag/AgBr interfacial catalyst that enables highly selective electro-oxidation of glycerol to formic acid. By integrating electronic modulation from Cu with the unique surface characteristics introduced by AgBr, this catalyst promotes efficient C–C bond cleavage and suppresses overoxidation, thereby achieving enhanced Faradaic efficiency toward formic acid under alkaline conditions. Comprehensive electrochemical and spectroscopic analyses reveal the synergistic role of the AuCu-Ag/AgBr interface in steering product selectivity and catalytic performance. Repeated electro-oxidation cycles confirmed the catalyst’s high stability, and the system also displayed broad applicability toward other polyols, such as 1,2-propanediol and ethylene glycol. These results highlight the potential of multiphase interfacial engineering in designing robust and selective electrocatalysts for the sustainable valorization of biomass-derived feedstocks.

2. Results

2.1. Physicochemical Properties of Catalysts

2.1.1. XRD Analysis

The Au-Ag/AgBr, Cu-Ag/AgBr, and AuxCuy-Ag/AgBr catalysts were synthesized via a co-reduction strategy, enabling the in situ growth of bimetallic and trimetallic nanoparticles on the AgBr support (see ESI† for detailed synthetic procedures and Figure S1).
The catalyst structures were subsequently probed by X-ray diffraction (XRD) analysis, and the associated diffraction patterns are presented in Figure 1a. XRD patterns reveal that the AuxCuy-Ag/AgBr catalyst exhibits characteristic diffraction peaks at 2θ values of 38.4°, 44.5°, 64.7°, and 77.8°, corresponding to the (111), (200), (220), and (311) planes of face-centered cubic (fcc) Au (JCPDS No. 04-0784) and the (111) and (311) crystal planes of Ag (JCPDS No. 03-0921). Compared to pure Au, the (111) peak of Au in the ternary catalyst shifts toward a higher 2θ angle, indicating the formation of an AuCu alloy. Additionally, distinct peaks observed at 2θ values of 30.9°, 44.3°, 55.0°, and 73.2° are indexed to the (200), (220), (222), and (420) planes of AgBr (JCPDS No. 79-0149), confirming the successful synthesis of the AgBr support and the reduction in AuCl4− and Cu2+ precursors to their metallic states. For comparison, the XRD pattern of the Cu-Ag/AgBr catalyst displays characteristic peaks attributable to metallic Ag, suggesting partial reduction from Ag+ to Ag0 during synthesis. In contrast, the AgBr signals in the Cu-Ag/AgBr sample are significantly diminished, implying a more extensive reduction from Ag+ to metallic Ag in the presence of Cu species. In addition, the crystallite sizes of the Au (111) facet for Au1Cu1-Ag/AgBr, Au2Cu1-Ag/AgBr, Au1Cu2-Ag/AgBr, and Au-Ag/AgBr were calculated using the Scherrer equation to be 13.4 nm, 17.6 nm, 6.9 nm, and 21.6 nm, respectively. The results indicate a gradual decrease in particle size with increasing Cu content, demonstrating that Cu incorporation effectively suppresses the aggregation of Au nanoparticles.

2.1.2. Elemental Composition and Chemical State Analysis

X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface composition and valence states of the Au1Cu1-Ag/AgBr catalyst. As shown in Figure S2 and Table S1, distinct signals corresponding to Au, Cu, Ag, and Br elements were clearly detected. The deconvolution of the Au 4f spectrum shows four components, with the lower binding energy doublet (83.7 eV for 4f7/2 and 87.4 eV for 4f5/2) representing metallic gold (Au0), and the higher energy doublet (84.1 eV for 4f7/2 and 87.7 eV for 4f5/2) indicating the presence of Au+ species (Figure 1b). In the Cu 2p region, peaks at 932.2 eV and 951.8 eV are assigned to metallic Cu0, while additional peaks at 934.4 eV and 954.3 eV correspond to Cu2+ 2p3/2 and 2p1/2, respectively, confirming the partial presence of Cu in an oxidized state (Figure 1c). Compared with previously reported binding energies of metallic Au, the Au0 4f peaks exhibit a positive shift of 0.2 eV (4f7/2) and 0.1 eV (4f5/2) [35], whereas the Cu0 peaks show negative shifts of 0.1 eV and 0.4 eV, respectively. These shifts in binding energy provide strong evidence for the formation of an AuCu alloy, likely due to electronic interactions between the two metals. In the Ag 3d region, the characteristic peaks at 368.0 eV and 374.0 eV are attributed to Ag+ 3d5/2 and 3d3/2, respectively, while weak signals at 368.6 eV and 374.6 eV suggest the presence of a small fraction of metallic Ag0 (Figure 1d). For the Br 3d region, two peaks centered at 67.9 eV and 68.9 eV are assigned to Br 3d5/2 and Br 3d3/2 (Figure S3), respectively. These XPS results confirm the successful formation of AuCu alloy nanoparticles along with Ag nanoparticles on the AgBr support, which is consistent with the XRD data. The XPS shifts also indicate charge redistribution among Au, Cu, and Ag, which is expected to shift the d-band center. Such an electronic modulation can optimize the adsorption strength of glycerol oxidation intermediates, thereby accounting for the enhanced catalytic activity. In addition, the metal ratios of the catalysts were characterized by ICP-OES. For all catalysts, the experimental Au/Cu ratios were in close agreement with the theoretical values (Table S2).

2.1.3. TEM Analysis

Transmission electron microscopy (TEM) images reveal that the Au1Cu1-Ag/AgBr catalyst consists of AuCu alloy nanoparticles and metallic Ag nanoparticles uniformly dispersed on AgBr nanosheet supports, and the average particle size is 62.9 nm (Figure 2a). High-resolution TEM (HRTEM) analysis shows a lattice spacing of 0.288 nm, which corresponds to the (200) plane of AgBr. The lattice fringes measured from the nanoparticles on the Au1Cu1-Ag/AgBr surface are 0.226 nm and 0.194 nm, which can be assigned to the (111) and (200) planes of the AuCu alloy, respectively, while the 0.235 nm spacing corresponds to the (111) plane of metallic Ag (Figure 2b). In contrast, the Cu-Ag/AgBr catalyst exhibits a sea urchin-like morphology, and the average particle size is 30.0 nm (Figure 2c). Lattice spacing of 0.279 nm observed from the protruding features corresponds to the (200) plane of AgBr (Figure 2d). For the Au-Ag/AgBr sample, spherical hollow particles with an average diameter of ~0.69 μm are observed, indicating severe aggregation of Au particles in the absence of Cu (Figure 2e,f). These results suggest that Cu plays a crucial role in forming a stable AuCu alloy and in suppressing nanoparticle aggregation. Simultaneously, the in situ grown AgBr nanosheets and Ag nanoparticles facilitate uniform dispersion of the AuCu nanoparticles and contribute to the formation of well-defined catalytic interfaces. To validate this hypothesis, water contact angle measurements were performed. The AuxCuy-Ag/AgBr catalyst exhibited a slightly smaller contact angle, allowing the liquid to spread more readily across the surface (Figure S4). This improved wettability facilitates better contact between the glycerol and active sites, thereby enhancing mass transport and catalytic efficiency [36].

2.2. Electro-Oxidation of Glycerol

2.2.1. Catalyst Screening Experiments

The electrocatalytic performance of the catalysts toward glycerol oxidation was first evaluated by linear sweep voltammetry (LSV) curves (Figure 3a). All catalysts exhibited measurable activity for the glycerol electro-oxidation reaction (GOR). Notably, the Au1Cu1-Ag/AgBr catalyst exhibited the lowest onset potential (0.45 V) and achieved a high current density of 32 mA cm−2 at 1.43 V, indicating superior catalytic activity. And the current density showed almost no decline even when crude glycerol was used as the feedstock (Figure S5). After the addition of glycerol, the redox peaks of the catalysts shifted to lower potentials. This suggests that, even if the intrinsic Au/Ag redox features may contribute, the observed shift still indicates that the catalysts exhibit a superior oxidation capability toward GOR compared with the OER [36]. When the Cu content was reduced, as in the Au2Cu1-Ag/AgBr sample, the onset potential shifted to 0.7 V, and a lower peak current density of 23 mA cm−2 was observed at 1.4 V. In contrast, the monometallic Au-Ag/AgBr and Cu-Ag/AgBr catalysts exhibited significantly higher onset potentials (~1.0 V) and lower peak current densities (~20 mA cm−2 at 1.2 V), followed by a rapid decline in activity. This behavior closely resembled that of Au1Cu1-Ag/AgBr tested in 1 M KOH without glycerol (Figure 1b). The superior performance of the AuCu alloy relative to its monometallic counterparts can be attributed to synergistic electronic and geometric effects between Au and Cu, which enhance the adsorption and activation of glycerol molecules. Comparable catalytic systems and benchmark Pd/C catalyst for glycerol to formic acid electroconversion are compiled in Table S3 and Figure S6.
To further probe the intrinsic activity of the catalysts, the electrochemically active surface area (ECSA) was estimated to be in the non-faradaic region (Figure 3c,d and Figure S7). The Au1Cu1-Ag/AgBr catalyst displayed the highest ECSA (144 cm2 g−1), followed by Au2Cu1-Ag/AgBr (131 cm2 g−1). In contrast, Cu-Ag/AgBr showed the lowest ECSA (53 cm2 g−1), only one-third that of Au1Cu1-Ag/AgBr. These results indicate that tuning the Au/Cu ratio effectively modulates the active surface area, with Au playing a dominant role in catalytic surface exposure and overall activity. Electrochemical impedance spectroscopy (EIS) measurements were performed at open-circuit potential for the catalysts with different metal ratios. The Au1Cu1-Ag/AgBr catalyst exhibited the smallest semicircle diameter, indicating the fastest charge-transfer efficiency (Figure S8). In addition, the turnover frequency (TOF) of Au1Cu1-Ag/AgBr was significantly higher than that of the other catalysts with the same atomic ratio (Figure S9), further confirming that Au1Cu1-Ag/AgBr is the most efficient catalyst.
To identify the optimal catalyst, long-term chronoamperometry tests were conducted under ambient conditions (Figure 3e). Among all samples, Au1Cu1-Ag/AgBr exhibited the highest catalytic activity and stability, achieving a glycerol conversion of 38% and a formic acid selectivity of 81% (Figure 3f). Au2Cu1-Ag/AgBr showed slightly reduced activity but maintained comparable selectivity toward formic acid. Interestingly, Au1Cu2-Ag/AgBr achieved the highest formic acid selectivity (90%), but at the expense of glycerol conversion, which was significantly lower. In contrast, Cu-Ag/AgBr exhibited poor formic acid selectivity (<50%), accompanied by increased formation of other byproducts. These results suggest that both Au and the AgBr support play crucial roles in facilitating C–C bond cleavage, while optimal Au content improves catalyst stability and promotes the selective formation of formic acid [37].

2.2.2. Effect of Single Reaction Parameter

Given its outstanding performance, the Au1Cu1-Ag/AgBr catalyst was selected for further investigating the influence of temperature and reaction time. The electrocatalytic performance of Au1Cu1-Ag/AgBr were performed at an elevated temperature (40 °C) for 8 h. As shown in Figure 1a, the current density at 1.43 V increased markedly to 71 mA cm−2, which is approximately 2.2 times higher than that observed at room temperature. This enhancement can be attributed to the endothermic nature of glycerol oxidation, where elevated temperatures accelerate glycerol adsorption and improve overall reaction kinetics [38]. Electrolysis experiments conducted at 1.23, 1.33, and 1.43 V under both room temperature and 40 °C conditions (Figure 3g) further corroborated this behavior. While increasing potential had a limited impact on glycerol conversion at room temperature, it significantly influenced product selectivity (Figure 3h). At lower potentials, glycolic acid dominated (selectivity: 44%) with formic acid as a minor product (31%). At 1.43 V, glycerol conversion reached 38% with 81% selectivity toward formic acid. Under 40 °C conditions, the catalytic performance improved significantly, achieving a conversion of 66% at 1.43 V, an increase of nearly 28% compared to room temperature. The product distribution remained similar, with a slight decline in formic acid selectivity (76%). These results indicate that higher potentials promote C–C bond cleavage, while elevated temperatures enhance catalyst activity without compromising product selectivity.
To further evaluate the electrocatalytic performance of the Au1Cu1-Ag/AgBr catalyst under varying potentials and reaction durations, i-t tests were conducted at 40 °C across a potential range of 1.23–1.43 V, followed by liquid-phase analysis of glycerol conversion and product distribution. At lower potentials, glycerol conversion gradually increased with extended reaction time, reaching 50% after 12 h. The product distribution remained relatively stable throughout the process, with glycolic acid as the dominant product, consistent with previously reported oxidation behavior of Au-based catalysts (Figure 4a) [39]. As the applied potential was increased to 1.33 V, both glycerol conversion and selectivity toward formic acid improved significantly. The selectivity of formic acid reached approximately 70%, while tartronic acid, an intermediate product, was no longer detected (Figure 4b). At an even higher potential of 1.43 V, the catalyst demonstrated further enhancement in both conversion and selectivity, achieving an 82% glycerol conversion and 74% formic acid selectivity after 12 h (Figure 4c).
To gain deeper insight into the mechanistic evolution of products during electro-oxidation, both in situ Raman spectroscopy and HPLC were employed. No reactive C3 intermediates, such as glyceraldehyde and 1,3-dihydroxyacetone, were detected; only glyceric acid, lactic acid, tartronic acid, and glycolic acid were observed. Temporal variations in the Raman bands at ~1060 cm−1 and ~1400 cm−1 were observed at 1.43 V, which can be attributed to carbonate species formed via overoxidation of intermediate carboxylates (Figure 4d). These assignments are supported by the previous literature on the Raman signatures of similar species [36,37,40,41]. The combination of these two techniques provides mutually supporting evidence for the mechanistic evolution of products during electro-oxidation [40,41]. In our system, glycerol electro-oxidation proceeds via a complex pathway involving multiple C–C and C–H bond cleavage and intermediate oxidation steps. The presence of a multiphase interface formed by Au1Cu1 alloy, Ag, and AgBr is key in modulating the adsorption and activation behavior of glycerol molecules. Based on the product distribution and spectroscopic evidence, a plausible reaction pathway is proposed (Figure 4e), in which glycerol is initially oxidized to glyceric acid, followed by transformation into tartronic acid. At elevated potentials, glyceric acid undergoes selective C–C bond cleavage to yield glycolic acid and formic acid, with part of the glycolic acid further oxidized to formic acid. These results highlight the essential roles of both Au species and the AgBr support in promoting C–C bond cleavage and stabilizing the reaction intermediates, while the optimal Au/Cu ratio not only improves the structural stability of the catalyst but also enhances the selective formation of formic acid under mild alkaline conditions. Altogether, these findings underscore the superior performance of Au1Cu1-Ag/AgBr as a robust and selective catalyst for sustainable glycerol valorization.

2.2.3. Substrate Scope Investigation

To evaluate the stability of the Au1Cu1-Ag/AgBr electrocatalyst, i-t cycling tests were conducted at 1.43 V and 40 °C (Figure 5a). During the initial 8 h reaction period, the current density rapidly decreased to approximately 23 mA cm−2 and then remained steady, resulting in a glycerol conversion of 66% (Figure 5b). Upon replenishing the cell with fresh electrolyte, the initial current density, glycerol conversion, and product distribution remained largely unchanged across two additional cycles. These results indicate that the observed current decrease was primarily due to the depletion of glycerol in the electrolyte, rather than catalyst deactivation. Post-electrochemical reaction analyses revealed negligible metal loss (<6 wt% for all elements), consistent with the high activity retention observed in the recycling tests (Figure 5a and Table S2). These results indicate that the catalyst design strategy effectively maximizes catalytic performance per unit mass of noble metal, thereby enhancing the utilization efficiency of Au and Ag. Furthermore, the demonstrated recyclability and electrochemical stability suggest a prolonged operational lifetime, alleviating concerns over the scarcity and high cost of noble metals. The remarkable cycling stability is likely due to the favorable adsorption of glycerol molecules on the multiphase interface. Furthermore, the AgBr nanosheets play a critical role in preventing nanoparticle aggregation during synthesis, thereby promoting uniform dispersion and maximizing the exposure of active catalytic sites.
To evaluate the general applicability of Au1Cu1-Ag/AgBr catalyst in the electrocatalytic oxidation of various polyols, the electro-oxidation of 1,2-propanediol and ethylene glycol were also conducted. As shown in Figure 5a, at 40 °C and 1.43 V, both polyols exhibited oxidation activity comparable to that of glycerol, with current densities reaching 42 mA cm−2 for 1,2-propanediol and 35 mA cm−2 for ethylene glycol (Figure 5c). Following 8 h of electrolysis at 1.43 V, the electro-oxidation of 1,2-propanediol showed similar catalytic stability to that of glycerol, achieving a conversion of 52%, albeit with slightly lower activity (Figure 5d and Figure S6). The primary oxidation product was formic acid (53% selectivity), consistent with the glycerol substrate. Acetic acid was identified as the main byproduct (33%), along with a small amount of lactic acid (Figure 5c). These results suggest that the Au1Cu1-Ag/AgBr catalyst effectively promotes C–C bond cleavage in 1,2-propanediol, particularly between the two adjacent hydroxyl-bearing carbon atoms, leading to acetic acid formation, which may further undergo partial cleavage to form formic acid. This mechanistic difference is likely attributable to the cooperative role of the Au and AgBr components at elevated potentials, which facilitates C–C bond scission and favors the generation of C1 products. Under the same reaction conditions, using ethylene glycol as the substrate resulted in a conversion of 41%. The dominant product was glycolic acid, with a selectivity of 62%, while formic acid accounted for the remaining 38% (Figure 5d).
Notably, the selectivity toward glycolic acid was reduced, while formic acid selectivity increased, further supporting that the interface structure at high potential enhance C–C bond cleavage in C2 polyols. However, when compared with the product distributions obtained from glycerol and 1,2-propanediol, the C–C bond cleavage capability of Au1Cu1-Ag/AgBr toward ethylene glycol appeared to be weaker. This indicates that ethylene glycol oxidation primarily proceeds via hydroxyl oxidation to glycolic acid rather than C–C bond scission to form formic acid, highlighting substrate-dependent reaction pathways under the tested conditions (Figure 5e).

3. Materials and Methods

3.1. Reagents and Materials

Silver nitrate (AgNO3, 99.8%), glycerol (C3H8O3, GLY, 99%), 1,2-propanediol (C3H8O2, 1,2-PDO, 99.5%), ethylene glycol (C2H6O2, EG, 99.7%), glyceric acid (C3H6O4, GLA, 98%), lactic acid (C3H6O3, LA, 99.5%), tartronic acid (C3H4O5, TA, 99%), pyruvic acid (C3H4O3, PA, 98%), glycolic acid (C2H4O3, GCA, 98%), acetic acid (CH3COOH, AA, 99.5%), oxalic acid (H2C2O4, OA, 99.5%), formic acid (HCOOH, FA, 88%), hydrochloric acid (HCl, 99.5%), sulfuric acid (H2SO4, 98%), ascorbic acid (C6H8O6, 99.7%), potassium hydroxide (KOH, 85%), potassium bromide (KBr, 99%), absolute ethanol (C2H6O, 99.7%), and acetone (C3H6O, 99.5%) were all purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Chloroauric acid trihydrate (HAuCl4·3H2O, 99.5%), copper(II) sulfate pentahydrate (CuSO4·5H2O, 99.5%), and polyvinylpyrrolidone (PVP, K30) were obtained from Macklin Biochemical Co., Ltd. (Shanghai, China) The commercial Pd/C catalyst was purchased from Wuhu Owl Technology Materials Co., Ltd. (Wuhu, China). All chemicals were used as received without further purification, and deionized water was used in all experiments.
Toray carbon paper (TGP-H-060, Tokyo, Japan) was hydrophobically treated, cut into uniform rectangular pieces of 2 × 2.5 cm2, and used as the working electrode substrate. Anion exchange membranes (AMI-7001, Membrane International Inc., Ringwood, NJ, USA) with a diameter of 3 cm were pretreated by immersion in a solution of 0.1 M glycerol and 1 M KOH for 24 h prior to use. Nafion solution (D520) was obtained from DuPont (Wilmington, DE, USA). Glassy carbon electrodes (Ø = 3 mm), electrode holders, graphite rods (Ø = 3 mm), platinum foil electrodes (1 × 1 cm2), Hg/HgO reference electrodes, and electrochemical cells were all purchased from Tianjin Aida Hengsheng Technology Development Co., Ltd. (Tianjin, China).

3.2. Catalyst Synthesis

The carbon paper was cut into 3 × 1.5 cm pieces and sequentially cleaned with 3 M hydrochloric acid, anhydrous ethanol, and deionized water. followed by drying at 45 °C overnight to obtain the processed carbon paper (CP).
AuxCuy-Ag/AgBr catalysts were synthesized via a co-reduction method using ethylene glycol and ascorbic acid as dual reducing agents. Specifically, 0.6 g of polyvinylpyrrolidone (PVP) and 1.2 g of ascorbic acid were dissolved in 100 mL of ethylene glycol under continuous stirring. The resulting solution was heated in a water bath at 85 °C and maintained for 10 min. Subsequently, 24 mL of an aqueous solution of CuSO4·5H2O (11.3 mM) was slowly added dropwise. The solution color rapidly changed to brick red, indicating the formation of reduced copper species. After 1 h of reaction, 24 mL of KBr aqueous solution (0.35 M) was introduced and stirred for an additional 10 min. Then, 12 mL of an aqueous solution containing HAuCl4·3H2O (22.6 mM) and AgNO3 (22.6 mM) was slowly added dropwise under vigorous stirring. The reaction was allowed to proceed for 1.5 h. After completion, stirring was stopped and the mixture was naturally cooled to room temperature. The resulting product was collected and washed alternately with absolute ethanol and acetone seven times to remove residual reactants. The purified catalyst was dried in a vacuum oven at 40 °C for 12 h to obtain the Au1Cu1-Ag/AgBr catalyst, with a nominal atomic ratio of Au to Cu of 1:1.

3.3. Catalyst Characterization

The composition and crystal structure of the samples were characterized by Kα-ray diffraction (XRD, SmartLab, Rigaku, Tokyo, Japan) using a Cu radiation source equipped with a Ni filter, Cu target radiation (λ = 0.154 nm), a scanning rate of 10° min–1, and an angular range of 2θ of 10–80°. The catalysts, which were homogeneously dispersed in anhydrous ethanol, were dripped onto a Cu grid and dried overnight, and then the morphology of the catalysts was imaged using a transmission electron microscope (TEM, HT-7800, Hitachi, Tokyo, Japan) in order to visualize the shapes and sizes of the catalysts. The catalyst microscopic images were captured using a high-resolution transmission electron microscope (HRTEM, TF-G20, Thermo Fisher Scientific, Waltham, MA, USA) and analyzed using Gatan Digital Micrograph 3 software to observe the microstructure of the nanoparticles and the crystal information. X-ray photoelectron spectroscopy (XPS, ESCALAB 250XI, Thermo Fisher Scientific, USA) was used to investigate the surface composition and valence states of Au1Cu1/AgBr samples using a monochromatic Al Ka source (1486.6 eV). After calibrating the binding energy through the C1s peak at 284.8 eV, XPS curves were fitted using XPS PEAK4.1 software. The water droplet contact angle was measured using an optical contact angle goniometer (CA, KSV CM200, Attension, Espoo, Finland) with an accuracy of 0.1°. In situ Raman spectroscopy measurements were performed using an HRS-5A spectrometer (Ocean Optical Instruments, Shanghai, China) with a 785 nm excitation wavelength and a 50% neutral density filter (laser power: 100 mW). The in situ electrochemical–Raman coupling experiments were conducted at room temperature in a custom-designed quartz electrochemical cell (C031-1, Gaoss Union, Tianjin, China) with a single-compartment, three-electrode configuration controlled by an electrochemical workstation. The catalyst-loaded carbon paper, Pt wire, and Hg/HgO electrode served as the working electrode, counter electrode, and reference electrode, respectively. The vertical beam from the instrument was converted to a parallel beam focused on the surface of the loaded carbon paper. Spectra were collected over 30 consecutive scans with an acquisition time of 5 s per scan, covering the range from 950 to 1500 cm−1 at a resolution of 0.65 cm−1. The metal contents of the catalysts were determined using inductively coupled plasma-atomic emission spectrometry (ICP-AES, model Optima 7300DV, PerkinElmer, Waltham, MA, USA).

4. Conclusions

A series of AuCu alloy nanoparticles and Ag nanoparticles were in situ grown on AgBr nanosheets via a solution-phase reduction strategy to construct an efficient electrocatalyst for polyol oxidation. The catalyst exhibited excellent capability in oxidizing terminal hydroxyl groups and promoting C–C bond cleavage, thereby enabling the selective formation of monocarboxylic acids from various polyol substrates. Electrochemical evaluations of catalysts with different Au/Cu atomic ratios demonstrated that the Au1Cu1-Ag/AgBr catalyst exhibited the highest activity and stability. Under ambient conditions, glycerol electro-oxidation at 1.43 V for 8 h yielded a conversion of 38% and a formic acid selectivity of 81%. Upon optimizing the reaction parameters, the best performance was achieved at 40 °C and 1.43 V over 12 h, reaching a glycerol conversion of 82% with a formic acid selectivity of 74%. Recycling tests confirmed the high stability of the catalyst under prolonged electrolysis. Furthermore, Au1Cu1-Ag/AgBr also demonstrated excellent electrocatalytic performance toward the oxidation of other polyols, such as 1,2-propanediol and ethylene glycol, confirming its broad applicability.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15090831/s1. Refs. [42,43,44,45,46,47,48] are cited in the Supplementary Materials.

Author Contributions

Conceptualization, investigation, writing—original draft, J.J.; writing—original draft, L.S. (Luyao Sun); visualization, methodology, Z.W.; validation, methodology, S.L.; supervision, writing—reviewing and editing, co-corresponding author, L.S. (Lingqin Shen) and H.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Zhenjiang Science and Technology Plan (GJ2024001).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) XRD patterns of AuCu-Ag/AgBr catalysts with different metal atomic ratios, Au-Ag/AgBr catalyst and Cu-Ag/AgBr catalyst (inset: magnified view of the Au (111) peak in the catalyst), (b–d) XPS spectra of the (b) Au 4f, (c) Cu 2p, and (d) Ag 3d orbitals in the Au1Cu1-Ag/AgBr catalyst.
Figure 1. (a) XRD patterns of AuCu-Ag/AgBr catalysts with different metal atomic ratios, Au-Ag/AgBr catalyst and Cu-Ag/AgBr catalyst (inset: magnified view of the Au (111) peak in the catalyst), (b–d) XPS spectra of the (b) Au 4f, (c) Cu 2p, and (d) Ag 3d orbitals in the Au1Cu1-Ag/AgBr catalyst.
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Figure 2. (a) TEM and (b) HRTEM images of the Au1Cu1-Ag/AgBr catalyst, (c) TEM and (d) HRTEM images of the Cu-Ag/AgBr catalyst, and (e) TEM and (f) HRTEM images of the Au-Ag/AgBr catalyst. Inset: particle size distribution.
Figure 2. (a) TEM and (b) HRTEM images of the Au1Cu1-Ag/AgBr catalyst, (c) TEM and (d) HRTEM images of the Cu-Ag/AgBr catalyst, and (e) TEM and (f) HRTEM images of the Au-Ag/AgBr catalyst. Inset: particle size distribution.
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Figure 3. Catalytic performance of catalysts with different metal atomic ratios: (a) LSV curves and (b) Au1Cu1-Ag/AgBr with or without 0.1 M GLY in 1 M KOH at a scan rate of 10 mV s−1 at room temperature; (c) linear fit plots between current density and scan rate for all catalysts; (d) calculation of ECSA for catalysts with different metal atomic ratios, catalytic performance of catalysts with different metal atomic ratios: (e) i-t curves and (f) GLY conversion and product distribution, under the reaction conditions of 0.1 M GLY and 1 M KOH electrolyte, scan rate of 50 mV s−1, at 1.43 V; (g) Chronoamperograms of Au1Cu1-Ag/AgBr in 1 M KOH and 0.1 M GLY solution at different applied potentials; (h) products selectivity and GLY conversion under the catalysis of Au1Cu1-Ag/AgBr after 8 h for different applied potentials and temperature.
Figure 3. Catalytic performance of catalysts with different metal atomic ratios: (a) LSV curves and (b) Au1Cu1-Ag/AgBr with or without 0.1 M GLY in 1 M KOH at a scan rate of 10 mV s−1 at room temperature; (c) linear fit plots between current density and scan rate for all catalysts; (d) calculation of ECSA for catalysts with different metal atomic ratios, catalytic performance of catalysts with different metal atomic ratios: (e) i-t curves and (f) GLY conversion and product distribution, under the reaction conditions of 0.1 M GLY and 1 M KOH electrolyte, scan rate of 50 mV s−1, at 1.43 V; (g) Chronoamperograms of Au1Cu1-Ag/AgBr in 1 M KOH and 0.1 M GLY solution at different applied potentials; (h) products selectivity and GLY conversion under the catalysis of Au1Cu1-Ag/AgBr after 8 h for different applied potentials and temperature.
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Figure 4. The influence of Au1Cu1-Ag/AgBr catalyst on the GLY conversion and product distribution with an electrolyte of 0.1 M GLY and 1 M KOH with different reaction times at reaction potentials of (a) 1.23, (b) 1.33, and (c) 1.43 V, respectively. (d) In situ Raman measurement under the catalysis of Au1Cu1-Ag/AgBr at 1.43 V for 30 min. (e) Reaction pathway of glycerol electrocatalytic oxidation reaction. Formic acid: FA; glyceric acid: GCA; glycolic acid: GLA; and lactic acid: LA.
Figure 4. The influence of Au1Cu1-Ag/AgBr catalyst on the GLY conversion and product distribution with an electrolyte of 0.1 M GLY and 1 M KOH with different reaction times at reaction potentials of (a) 1.23, (b) 1.33, and (c) 1.43 V, respectively. (d) In situ Raman measurement under the catalysis of Au1Cu1-Ag/AgBr at 1.43 V for 30 min. (e) Reaction pathway of glycerol electrocatalytic oxidation reaction. Formic acid: FA; glyceric acid: GCA; glycolic acid: GLA; and lactic acid: LA.
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Figure 5. Cyclic use of i-t curves (a), product selectivity and GLY conversion (b) under the catalysis of Au1Cu1-Ag/AgBr catalyst. Each cycle was conducted in 0.1 M GLY and 1 M KOH electrolyte, 0.93 V potential, reaction time of 8 h, and reaction temperature of 40 °C. (c) CV curves and (d) product selectivity (formic acid: FA; glyceric acid: GCA; glycolic acid: GLA; lactic acid: LA; tartronic acid: TA and acetic acid: AA) and substrate conversion (glycerol: GLY, 1,2-propanediol: 1,2-PDO, and ethylene glycol: EG) in electrolyte with 1 M KOH and 0.1 M GLY, 1,2-PDO or EG at 1.43 V, respectively, (e) reaction pathway of 1,2-PDO and EG electrocatalytic oxidation reaction.
Figure 5. Cyclic use of i-t curves (a), product selectivity and GLY conversion (b) under the catalysis of Au1Cu1-Ag/AgBr catalyst. Each cycle was conducted in 0.1 M GLY and 1 M KOH electrolyte, 0.93 V potential, reaction time of 8 h, and reaction temperature of 40 °C. (c) CV curves and (d) product selectivity (formic acid: FA; glyceric acid: GCA; glycolic acid: GLA; lactic acid: LA; tartronic acid: TA and acetic acid: AA) and substrate conversion (glycerol: GLY, 1,2-propanediol: 1,2-PDO, and ethylene glycol: EG) in electrolyte with 1 M KOH and 0.1 M GLY, 1,2-PDO or EG at 1.43 V, respectively, (e) reaction pathway of 1,2-PDO and EG electrocatalytic oxidation reaction.
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Jin, J.; Sun, L.; Wang, Z.; Li, S.; Shen, L.; Yin, H. Enhanced Electrocatalytic Performance for Selective Glycerol Oxidation to Formic Acid at a Multiphase AuCu-Ag/AgBr Interface. Catalysts 2025, 15, 831. https://doi.org/10.3390/catal15090831

AMA Style

Jin J, Sun L, Wang Z, Li S, Shen L, Yin H. Enhanced Electrocatalytic Performance for Selective Glycerol Oxidation to Formic Acid at a Multiphase AuCu-Ag/AgBr Interface. Catalysts. 2025; 15(9):831. https://doi.org/10.3390/catal15090831

Chicago/Turabian Style

Jin, Jianchuan, Luyao Sun, Zhiqing Wang, Shiyu Li, Lingqin Shen, and Hengbo Yin. 2025. "Enhanced Electrocatalytic Performance for Selective Glycerol Oxidation to Formic Acid at a Multiphase AuCu-Ag/AgBr Interface" Catalysts 15, no. 9: 831. https://doi.org/10.3390/catal15090831

APA Style

Jin, J., Sun, L., Wang, Z., Li, S., Shen, L., & Yin, H. (2025). Enhanced Electrocatalytic Performance for Selective Glycerol Oxidation to Formic Acid at a Multiphase AuCu-Ag/AgBr Interface. Catalysts, 15(9), 831. https://doi.org/10.3390/catal15090831

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