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Interface-engineering of the Catalysts for Efficient Electrocatalytic
Upcycling of Polyethylene Terephthalate Waste
Jing Liu1, Xiang Peng1*
1

Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, School of Materials Science and Engineering, Wuhan
Institute of Technology, Wuhan, Hubei Province, China*

Correspondence to: Xiang Peng, PhD, Professor, Hubei Key Laboratory of Plasma Chemistry and Advanced Materials,
School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan, 430205, Hubei Province, China;
E-mail: xpeng@wit.edu.cn

Abstract

Plastics have become an essential component of our daily lives, but theirwidespread use has resulted in significant environmental and ecologicalpollution. Conventional methods for plastic waste treatment are both environmentally unfriendly and energy-intensive. In recent years, the emergence ofelectrocatalytic degradation technology for plastic waste has opened up new
possibilities for converting waste plastics into valuable chemicals, thus promoting
the realization of a circular economy for plastics. This review aims to provide an
in-depth overview of the fundamental principles and characteristics of interfaces,
focusing on the electrocatalytic degradation of ethylene glycol (EG) derived frompolyethylene terephthalate (PET). This review primarily examines the two primarymethods of electrocatalytic oxidation reactions of PET-derived EG, along with theadvancements in interface engineering technology. It delves into the research
progress made in interface catalysts for the electrocatalysis of PET-derived
EG, while also discussing future research directions. The objective is to delve
deeper into the development of effective electrocatalytic degradation catalysts,
to address the pressing challenges posed by the ecological environmental crisisand the imperative need for transforming and upgrading PET plastic waste.
Keywords: electrochemical upcycling, electrocatalysis, polyethylene terephthalate (PET), ethylene glycol, interface engineering

1 INTRODUCTION
The rapid growth of the modern economy and society
has resulted in an unprecedented increase in fossil fuelconsumption, causing severe damage to our ecologicalenvironment[1]. Simultaneously, the fast-paced natureof our lives has led to the ubiquitous presence ofdisposable plastic products[2,3]. Each plastic container isfurnished with a distinctive identification sign resemblingan “ID card”, typically positioned at the base. Enclosed
within a triangular shape, a number ranging from 1 to
7 is displayed, with each number denoting a particular
type of plastic material. The numbers are as follows:#1: polyethylene terephthalate (PET/PETE), #2: high-Published by Innovation Forever Publishing Group Limited

Received: January 11, 2024
Revised: February 6, 2024
Accepted: February 20, 2024
Published: March 15, 2024
Copyright © 2024 The Author(s).
This open-access article is licensed
under a Creative Commons Attribution
4.0 International License (https://creativecommons.org/licenses/
by/4.0), which permits unrestricted
use, sharing, adaptation, distribution,and reproduction in any medium,provided the original work is properly
cited.
Citation: Liu J, Peng X. Interfaceengineering of the Catalysts for
Efficient Electrocatalytic Upcycling of
Polyethylene Terephthalate Waste.
Innov Discov, 2024; 1(1): 1.

density polyethylene (HDPE), #3: polyvinyl chloride(PVC), #4: low-density polyethylene (LDPE), #5:
polypropylene (PP), #6: polystyrene (PS), and #7:
others such as acrylonitrile butadiene styrene (ABS)[4-8].
Plastic pollution, also known as white pollution[9,10],
refers to the solid waste formed when high molecularcompound plastics like PP and PET are carelessly
discarded after use, resulting in adverse visual effects
and substantial ecological damage and may evenendanger human health[11,12]. This further exacerbates
the challenges associated with subsequent disposal[13].
Consequently, the imperative to ban and restrict plastic
usage has become increasingly urgent[14].

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Liu J et al. Innov Discov 2024; 1(1): 1
PET plastic, as a main type of plastic that is frequently
contacted and used in daily life, undoubtedly brings
great convenience to people. However, at the sametime, the massive use of PET has also produced serious
pollution problems for the environment[15]. To address
the environmental pollution caused by PET, researchers
have focused on developing efficient degradation
methods. Currently, the primary methods for PET
waste disposal involve chemical recycling and physicalrecycling[16]. Physical recycling entails crushing, cleaning,and drying PET waste to produce raw materials.
However, the quality of the recycled products often
falls short of the original raw material standards[17], andthe treatment process generates wastewater and gas,significantly impacting the environment. In contrast,
chemical recycling methods convert PET waste intomonomers or intermediates, offering the advantageof obtaining high-purity monomers[18,19]. Establishinga catalytic recycling system using chemical means
can help combat white pollution, reduce greenhousegas emissions, and yield valuable chemicals, thereby
offering economic benefits[20]. Among these chemical
recovery methods, electrocatalysis stands out asan electrochemical technique that has been widelyused in energy and environment applications[21-26].
Its application in PET plastic degradation enables
an efficient and environmentally friendly process,transforming PET degradation products into high-value
chemicals and fuels[27].
Consequently, electrocatalysis holds tremendous
potential, facilitating efficient PET waste recycling,
reducing environmental pollution, lowering greenhousegas emissions, and generating economic benefits[28].
This technology plays a crucial role in achieving asustainable circular economy for plastics. In recent
decades, the demand for efficient catalysts has
surged[29], leading to rapid advancements in interface
engineering catalysts for the electrochemical oxidation
reaction of ethylene glycol (EGOR) derived from PET.
However, comprehensive reviews on heterogeneousinterface engineering for this process are currently
lacking.
This review aims to present the PET depolymerization
methods and explore the fundamental principles ofelectrochemical conversion using PET-derived ethylene
glycol. Additionally, the mechanisms and applications ofinterface engineering in the electrochemical conversionof PET-derived ethylene glycol will also be summarized.
The primary goal is to provide a valuable reference forthe development of new electrocatalysts that exhibit
high efficiency, good selectivity, cost-effectiveness,and value addition. By adhering to principles of green
technology, environmental protection, and sustainable
development, we hope to contribute to the early
realization of the “plastic reduction and recycling” goal.
https://doi.org/10.53964/id.2024001

Figure 1. Molecular structure of PET.

2 FUNDAMENTALS OF PET DEPOLYMERIZATIONPET is a commonly used polymer, which has thechemical formula of (C10H8O4)n. When PET is spun into
fibers for fabrics, it is commonly referred to as “polyester”.
However, in container and packaging applications, it is
known as “PET” or “PETE”[30]. The molecular structureof PET consists of a linear macromolecule with hydroxyl
and carboxyl end groups connected by ester groups, witha benzene ring and an ethyl group positioned between
them. With its regular molecular chain and symmetry, PET
forms a linear macromolecule, as illustrated in Figure 1[31].
The PET molecule’s C-O bond typically possesses
lower chemical energy compared to the C-C bond[32].
Various external factors, including water, heat, light,
and oxygen, can cause the fracture of chemical bonds
in PET, leading to its degradation. PET depolymerization
methods are classified based on the chosen degradants,
which include alcoholysis, glycolysis, hydrolysis, andaminolysis. Figure 2 illustrates the categorization of these
depolymerization methods[33]. The primary depolymerized
products include terephthalic acid (TPA/PTA) and EG, aswell as combinations such as terephthalamide and EG,
dimethyl terephthalate and EG, and bis(2-hydroxyethyl)
terephthalate. These products can be obtained throughhydrolysis[34], ammonolysis[35], methanol alcoholysis[36],and EG alcoholysis (also known as glycolysis)[37].
PET is an abundant polyester plastic that can behydrolyzed into TPA and EG in aqueous solutions ofdifferent media[38]. These media include acidic[39],neutral[40], and alkaline solutions[41]. However, acidhydrolysis is highly corrosive to the reaction system andgenerates waste liquid containing inorganic salts andacidic waste. Neutral hydrolysis requires a large amountof water, resulting in low EG content in the product andmaking separation challenging. Alkaline hydrolysis, on
the other hand, allows for the precipitation of EG and TPA
by acidifying the product solution and adjusting the pH to2-3[42]. Thus, compared to acidic and neutral hydrolysis
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Liu J et al. Innov Discov 2024; 1(1): 1

Figure 2. Methods for PET depolymerization.

Figure 3. Two reaction paths of EGOR: (i) C-C cleavage pathways and (ii) C-C preservation pathways.

methods, alkaline hydrolysis offers advantages in termsof purification.
Electrocatalysis provides a promising approach forconverting PET-derived EG into high-value products
and recycling TPA[19]. In the electrocatalytic processof PET depolymerization, the oxidation current is
attributed to the oxidation of EG in PET rather thanTPA[43]. During electrocatalysis, there are typically tworeaction paths for EGOR, as shown in Figure 3[44]. The
https://doi.org/10.53964/id.2024001

C-C cleavage pathway leads to the formation of formic
acid (C1 product), while the C-C preservation pathway
results in the production of glycolic acid (C2 product).
By modulating the adsorption strength of carbonyl
intermediates on the catalyst surface, the C1/C2
reaction path can be controlled, enabling high selectivityof the EGOR products[45,46]. This means that the surface/interface structure of the catalysts can be tailored tofacilitate the electrocatalytic transformation of PETderived EG, enhancing product selectivity and yield.
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Liu J et al. Innov Discov 2024; 1(1): 1A

B

Figure 4. Reaction path of EGOR. A: Synchronous electrochemical conversion of anode PET hydrolysate with cathode CO2
to formic acid; B: Reaction path of the oxidation of ethylene glycol to formic acid. Reproduced from Ref.[47] with permission
from American Chemical Society.

In a study conducted by Zhao and Wang[47], earthabundant Ni and Co-based materials were employed
as anodic catalysts for the electrocatalytic oxidation of
PET-derived EG to produce formic acid. Simultaneously,
cathodic coupling electrolysis of CO2 was employed to
produce formic acid, as depicted in Figure 4A. Highperformance liquid chromatography analysis revealed
that the Faraday efficiency of formic acid remained
consistently above 90% when the anode potential
was maintained at 1.45V vs. the reversible hydrogenelectrode (RHE). These results demonstrated that the
NiCo2O4/carbon fiber paper catalyst exhibited remarkablestability and high selectivity for the electrochemicaltransformation of PET hydrolysate into formic acid.
To further investigate the reaction mechanism, an
additional experiment was conducted to study theoxidation of glycolic acid (GA)[47]. It was observed thatthe main product of the glycolic acid oxidation reaction
was oxalic acid, whereas the EGOR experiment primarily
yielded formic acid. This finding suggested that glycolicacid was not a crucial intermediate in the EGOR
catalyzed by the prepared NiCo2O4 electrocatalyst.
Therefore, the proposed reaction mechanism for the
EGOR on the NiCo2O4 electrocatalyst can be describedas follows: Initially, the −OH deprotonation step occurs,
https://doi.org/10.53964/id.2024001

leading to the formation of the reactive alkoxideintermediate OCH2−H2CO. Subsequently, the alkoxideintermediate undergoes oxidation to form the glyoxal
intermediate OCH−HCO, which then undergoes C-C
bond cleavage to yield formic acid. The by-product,
glycolic acid, is a result of the transformation of theCannizzaro reaction of glyoxal, and the reaction pathway
is illustrated in Figure 4B.
The selective oxidation of the hydroxymethyl groups
in EG to produce GA is highly desirable in EGOR as GA is
economically valuable and finds extensive applications
in various industries such as industrial applications, foodadditives, pharmaceuticals, and agriculture. The market
size of glycolic acid was $310.4 million in 2020 and is
expected to reach $531.5 million by 2027[42].
To achieve the selective oxidation of EG to GA, Chen etal.[48] designed and synthesized a Pd-Ni(OH)2 composite
electrocatalyst, as depicted in Figure 5A. Through thesynergistic interaction of Pd and Ni sites, ethylene
glycol can be highly selectively oxidized to glycolic acid
while generating hydrogen at the cathode. The catalyst
exhibited a high selectivity of 91.6% for glycolic acidwith an ethylene glycol conversion rate of 93.2%. Evenat an industrial-scale current density of 600mA·cm-2,
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Liu J et al. Innov Discov 2024; 1(1): 1A

B

Figure 5. The Pd-Ni(OH)2 catalyst for EGOR. A: Schematic diagram of the synthesis of Pd-Ni(OH)2 on nickel foam; B:
Optimal configuration of EG oxidation process on Pd-Ni(OH)2. Reproduced from Ref.[48] with permission from Wiley.

the catalyst maintained a high Faraday efficiency
and selectivity of approximately 85%. In-situ Fourier
Transform Infrared Spectroscopy during electrochemical
experiments revealed that OH species rapidly convert
the OC-CH2OH intermediate to glycolic acid products
instead of C1 products through the C-C cleavage
pathway. The electronic interaction between Pd andNi(OH)2 leads to a decrease in the d-band center shiftof Pd, reducing carbonyl adsorption and facilitating thetransfer of the OC-CH2OH intermediate from the active
Pd site to the adjacent Ni site. This interaction prevents
excessive cleavage or oxidation of the C-C bond. Basedon experimental results, the conversion pathway fromEG to GA can be summarized as follows: HOCH2-CH2OH→ HOCH2-CH2OH → HOCH2-CH2O(RO) → HOCH2-CHO* →HOCH2-CO* → HOCH2COOH* → HOCH2-COOH(GA), as
illustrated in Figure 5B. Their work not only provides
a promising approach for upgrading PET to high-value
glycolic acids at an industrial level but also offers valuable
insights into intermediate conversion pathways andcatalyst design with synergistic active sites.

3 CATALYSTS’ INTERFACE ENGINEERING FOR ELECTROCATALYTIC UPCYCLING OF PETDERIVED EG
3.1 Electrocatalytic Conversion of EG
to C1 Products
The surface and interface of catalysts encompass
the atomic layers on the surface and the junction
https://doi.org/10.53964/id.2024001

between phases, which do not have a well-definedboundary[49]. In the context of electrochemical reactions,the catalyst’s interface provides active centers forelectrocatalytic reactions and plays a crucial role inachieving high efficiency[50-52]. The interface can modify
the equilibrium relationship between reactants andproducts, thereby facilitating the reaction process. The
overall electrocatalytic reaction can be described inthree consecutive steps: Firstly, the chemical adsorptionof reactants occurs on the surface or interface ofthe electrocatalyst. Secondly, the reactants undergo
activation to generate intermediates. Lastly, the final
product is desorbed from the electrocatalyst into theelectrolyte[53,54]. The optimal performance of the entire
electrocatalytic process relies on the optimization of theadsorption and desorption steps.
The limited catalytic performance of non-precious
metal-based electrocatalysts hinders their widespreadindustrial application[55]. To overcome this limitation,
various strategies, such as interface engineering[56],
topography engineering[57], defect engineering[58], andcrystal plane engineering[59], have been employed
to enhance their electrocatalytic capability. Typically,
the active sites responsible for electrocatalysis areconcentrated at the edge sites; however, their number
is relatively limited, posing a significant obstacle toachieving high efficiency. The atomic and molecular
structure at the catalyst’s interface plays a crucialrole in determining the catalytic activity of these
active sites[60]. Atoms located at the interface exhibit aPage 5 / 12

Liu J et al. Innov Discov 2024; 1(1): 1A

BCFigure 6. Structure of the CoNi0.25P catalyst. (A-B): HR-TEM images of CoNi0.25P nanosheet; C: Schematic diagram of thestructural evolution of the CoNi0.25P catalyst under reaction conditions. Reproduced from Ref.[63] with permission from Springer
Nature.

coordination unsaturated state compared to bulk atoms,
making them highly susceptible to physisorption,
chemisorption, or direct chemical reactions with otherspecies, leading to the formation of new species.
Additionally, interface engineering holds great potential
for improving electrochemical performance by
optimizing the chemisorption of reaction intermediates,
enhancing electron/mass transport, and preventing
the aggregation of active components[61]. Therefore, apromising strategy to enhance the mass and energy
conversion of electrocatalytic reactions is to increase theexposure of edge active sites and enhance the intrinsic
activity of these sites through interface engineering of
the catalysts. This approach has emerged as a research
hotspot in the field of electrocatalysis[62].
Indeed, the electrocatalytic reforming of EG
encounters challenges such as a complex reaction
process, poor product selectivity, and catalyst
deactivation. To achieve the electrochemicalreforming of EG derived from PET in line with green
and sustainable development, the design of highperformance catalysts is crucial. In recent years,
interface engineering strategies have emerged as
effective approaches to enhance the electrocatalyticoxidation performance of PET-derived ethylene glycols,
making it a prominent research topic. By manipulating
the atomic and molecular structure at the interfaceof catalysts, interface engineering can optimize theadsorption of reaction intermediates, facilitate electron/
mass transport, and prevent the aggregation of active
components.
In a significant discovery from a previous study, it
https://doi.org/10.53964/id.2024001

was observed that secondary alcohols featuring a-C(OH)-C- structure can undergo oxidation, resulting
in the cleavage of the C-C bond when cobalt hydroxyloxide is employed as an anode catalyst in an alkaline
electrolyte. This intriguing process leads to theformation of carboxylic acid compounds. Building uponthis breakthrough, a team of researchers, under theleadership of Duan et al.[63] has successfully developed
a highly efficient bifunctional CoNi0.25P electrocatalyst.
This novel electrocatalyst serves as a pivotal component
in their proposed electrocatalytic strategy, which aims
to convert the hydrolyzed products of PET waste into
potassium dicarboxylate and terephthalic acid within a
KOH electrolyte.
In this electrochemical process, the CoNi 0.25P
catalyst catalyzes the conversion of EG at the anodeof the electrolytic cell, resulting in the formationof formate. Remarkably, the selectivity of thisreaction exceeds 90%. Simultaneously, hydrogenis generated at the cathode. In the absence of EG,
all electrocatalysts exhibit relative activity towards
the oxygen evolution reaction (OER) with an initialpotential of approximately 1.51V vs. RHE. However,with the introduction of 0.3M EG into the electrolyte,
the initial potential of all electrocatalysts shifts to lower
values (ranging from 1.22 to 1.33V vs. RHE). This
shift indicates that, thermodynamically, the oxidationof EG is more favorable compared to the OER. Highresolution transmission electron microscopy (HRTEM) observations revealed that the CoNi0.25P material
consists of small Ni2P nanoparticles interconnected with
CoP particles, forming a CoP-Ni2P heterostructure, as
depicted in Figure 6A-B. When utilized in an H-type
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Liu J et al. Innov Discov 2024; 1(1): 1A

BCFigure 7. The CoNi0.25P catalyst for EGOR. A: Polarization curves with 85% iR correction for organic oxidation in 1M KOH
with 0.3M substrate; B: Formate productivity at constant potential (1.5V vs. RHE) for different substrates; C: Proposed reaction route for electrocatalytic EG oxidation. Reproduced from Ref.[63] with permission from Springer Nature.

electrolyzer, the CoNi0.25P electrocatalyst demonstrates
its capability to generate a high current density of
approximately 350mA·cm-2 at a potential of 1.7V vs.
RHE. Moreover, when applied to a zero-gap membraneelectrode assembly with minimal energy loss, thecatalyst achieves a significant current density of up to
500mA·cm-2 at a 1.8V. These impressive results areaccompanied by a Faraday efficiency exceeding 80%
and a formate selectivity of more than 80%.
A comprehensive investigation was undertaken to
study the changes occurring in the CoNi0.25P catalyst
during electrochemical reactions. The findings revealed
that the catalyst retained the stability of its primarystructure during the hydrogen evolution reaction.
However, advanced characterization techniques
including HR-TEM and X-ray diffraction provided
evidence that the catalyst’s structure underwent
reconstruction during the anodic oxidation reaction.
This reconstruction resulted in the formation of alow crystalline metal oxy(hydroxide) analogue, as
illustrated in Figure 6C.
https://doi.org/10.53964/id.2024001

Moreover, the research team conducted an extensive analysis of the dynamic transformation ofintermediate products during the oxidation reactionof EG. To gain insights into the electrochemical andkinetic aspects, three different starting substrates
were evaluated: ethylene glycol, GA, and glycolic
aldehyde. The results unveiled that glycolaldehyde
exhibited a significantly faster reaction rate in theformation of formic acid compared to ethylene glycol
and glycolic acid, as illustrated in Figure 7A-B. Thisfinding highlights the crucial role of glycolaldehyde as
an intermediate in the formic acid formation process.
Based on the experimental findings, the researchers
proposed an oxidation mechanism for EG, which isillustrated in Figure 7C. According to the proposedmechanism, EG is initially oxidized to glycolaldehyde,
which undergoes rapid C-C cleavage to form formateions. Additionally, a minor portion of glycolaldehyde
is oxidized to glycolic acid, which then undergoes
a slower C-C cleavage process, ultimately leading
to the production of formic acid. This elucidation ofPage 7 / 12

Liu J et al. Innov Discov 2024; 1(1): 1
A

B

C

E

D

F

Figure 8. The Pt/γ-NiOOH/NF catalyst for EGOR. A: Schematic diagram of the preparation of Pt/γ-NiOOH/NF catalyst bycorrosion engineering; High-resolution XPS spectra of (B) Ni-2p, (C) Pt-4f, and (D) O-1s for the Pt/γ-NiOOH/NF, γ-NiOOH/NF,
and Pt/NF catalysts; E: Calculated charge difference isosurfaces at the Pt and γ-NiOOH interface; F: the Faraday efficiency, selectivity, and formation rate of glycolic acid at a fixed potential of 0.55V of the Pt/γ-NiOOH/NF (Pt mass loading of 0.18mg·cm-2),
Pt/NF, and Pt/C catalysts. Reproduced from Ref.[42] with permission from Wiley.

the oxidation mechanism provides valuable insightsthat contribute to a deeper understanding of the EG
oxidation reaction and its associated pathways.

3.2 Electrocatalytic Conversion of EG
to C2 Products
In a study conducted by Qiu et al.[42], the Pt/γ-NiOOH/
NF electrocatalyst was prepared through corrosion
engineering in the presence of K2PtCl4, NaCl, and nickel
foam, as depicted in Figure 8A[42]. X-ray photoelectron
spectroscopy (XPS) was employed to investigate thecoupling effect between Pt and NiOOH in the catalyst, asshown in Figure 8B-D. The researchers discovered thatthe binding energy of the Ni3+ signal in the Pt/γ-NiOOH/
NF catalyst was negatively shifted by 0.5eV comparedhttps://doi.org/10.53964/id.2024001

to that of γ-NiOOH/NF (Figure 8B). Additionally, thebinding energy of Pt-4f in Pt/γ-NiOOH/NF was positively
shifted by 0.3eV compared to Pt/NF (Figure 8C). These
shifts in the binding energy peaks of Ni and Pt indicate
the presence of electronic interaction between Pt andthe γ-NiOOH phases. The O-1s spectrum of Pt/γ-NiOOH/
NF in Figure 8D demonstrates the existence of Pt-ONi bonds, which are not observed in the γ-NiOOH/NF
catalyst. This finding serves as key evidence for theinteraction between Pt and γ-NiOOH. Furthermore,calculations of the charge difference in the catalyst
suggested that a significant amount of charge had
accumulated at the Pt/γ-NiOOH interface, as illustrated
in Figure 8E. Moreover, the calculated results indicatedthat the shortest oxygen-surface distance between EG
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Liu J et al. Innov Discov 2024; 1(1): 1A

B

Figure 9. Comparison of Pd and Pd-Ni(OH)2 catalysts for EGOR. A: Surface valence band photoemission spectra of Pd
and Pd-Ni(OH)2; B: CV curves of Pd-Ni(OH)2/NF, Pd/NF and Pd/C in 1 M KOH. Reproduced from Ref.[48] with permission fromWiley.

and Pt/γ-NiOOH was 1.8Å. This distance suggests thatthe interfacial region between EG and Pt/γ-NiOOH ishighly active for the adsorption of EG reactants.
The Pt/γ-NiOOH/NF catalyst successfully achieved theselective oxidation of EG from PET plastics to glycolicacid at a low potential of 0.55V vs. RHE. It achieved ahigh Faraday efficiency of 97.2% and a selectivity ofglycolate production of 98.2%. Additionally, the catalyst
demonstrated a production rate of 0.14mmol·cm-1·h-1,
as depicted in Figure 8F.
Both experimental and theoretical findings suggestthat the formation of glycolic acid involves three
deprotonation steps. The first step involves theformation of adsorbed 1,2-dihydroxy ethyl or 2-hydroxyethoxy species. In the second step, the adsorbed
2-hydroxyacetyl group is generated. Finally, in the third
step, the adsorbed glycolic acid is formed. Theoretical
calculations indicate that the production of the adsorbed
2-hydroxyacetyl species plays a crucial role in theformation of glycolic acid. The calculations reveal afree energy change of ΔG=0.33eV for the protonation
process at the Pt/γ-NiOOH interface, which is smaller
than the ΔG=1.14eV observed on the Pt surface. Thissuggests that the Pt/γ-NiOOH interface is favorable forthe production of glycolic acid.
Chen et al.[48] designed a synergistic catalyst of PdNi(OH)2/Ni foam (Pd-Ni(OH)2/NF) for the electrocatalyticoxidation reaction of EG to produce GA. Through charge
density difference and Bader charge calculations,they found 1.71 electrons were transferred from Pd
to Ni(OH)2, indicating a strong electronic interaction
between the two components. The reduced electron
density of Pd weakens the feedback effect of the Pd-3d
electrons on the CO 2π* orbitals, diminishing the bondstrength of the Pd-*CO species. To further investigate
the interfacial interactions, they employed surface
valence band photoelectron spectroscopy to evaluate
the d-band centers of Pd and Pd-Ni(OH)2. Compared tohttps://doi.org/10.53964/id.2024001

the d-band center of the Pd at -2.58eV, the Pd-Ni(OH)2
exhibited a downshifted d-band center at -3.14eV. This
downshift effectively weakens the binding strength ofthe carbonyl intermediate at the Pd site, as shown in
Figure 9A.
Furthermore, they conducted in-depth studies on
the adsorption and activation of OH species throughcyclic voltammetry (CV) tests. The experimental
results revealed that Pd-Ni(OH)2 had a lower onset
potential for OH adsorption/desorption peaks (0.4V vs.
RHE) compared to Pd/NF (0.5V vs. RHE), while Pd/C
demonstrated almost no peaks, as shown in Figure 9B.
This suggests that the oxygenophilic nature of Ni(OH)2
assists in efficiently oxidizing OH- on the Pd surface toform *OH adsorbed species. By combining the downshiftof the d-band center of the Pd and the enhanced
oxyphilicity of Ni, the interfacial interactions synergisticallyfacilitate the rapid desorption and transfer of GA from theactive Pd site to the inactive Ni site, thereby preventing
its over-oxidation.
Comparing different preparation processes for glycolic
acid, the electrochemical method utilizing EG derived
from PET plastic exhibits several advantages. These
include a high yield of glycolic acid, low reaction voltage,and low precious metal mass loading. These advantages
contribute to the economic viability of electrochemicalreforming of PET waste plastics for glycolic acidproduction.

4 CONCLUSIONS AND PROSPECTS
With the escalating accumulation and environmental
impact of plastic waste, research on plastic degradation
and recycling has gained significant importance. In thecontext of electrochemical reforming and upgrading of
PET waste, modification of catalyst surface interfaces
plays a crucial role. The catalyst surface interface, as
the region where gas, solid, and liquid phases interact,
directly influences catalytic activity and reaction selectivity. This review discusses the fundamentals of PETPage 9 / 12

Liu J et al. Innov Discov 2024; 1(1): 1
depolymerization including the structure of PET, thedecomposition mechanism as well as the decomposition
path and products of the PET. In addition, the research
progress of the catalysts’ interface engineering forelectrocatalytic upcycling of PET-derived EG has been
discussed detailedly from the perspectives of the type ofelectrocatalytic products, including C1 and C2 products.
The aim is to inspire further research ideas to tackle
the urgent challenges of the ecological environment
crisis and the transformation and upgrading of PET
plastic waste. Additionally, the review also analyzes andprovides prospects for the problems and solutions in thisfield.
(i) Catalyst design and optimization remain an
important area for future exploration. Researchers
can continue to investigate novel catalysts for theelectrocatalytic PET-derived ethylene glycol process,utilizing advanced computational methods andexperimental techniques to study the active centers,
surface structures, and lattice defects of catalysts,
thereby enhancing their activity and selectivity.
(ii) Interface engineering and regulation ofelectrocatalytic performance are crucial factors inelectrocatalytic processes. Future studies can focus on
exploring the effects of different interface materials andstructures on electrocatalytic performance. Suitable
methods can be developed to regulate electrontransport, proton transport, and mass transfer at theinterface, thereby improving the yield and purity of
ethylene glycol.
(iii) Application development for electrocatalytic
PET-derived ethylene glycol holds substantial potential
in areas such as the synthesis of high-value-added
compounds and energy conversion. Future research canintegrate electrocatalytic PET-derived ethylene glycol
technology with other related fields, such as combining
it with renewable energy sources like solar or wind
power to drive the process using green energy. This
integration can lead to the development of additional
applications and products, promoting sustainable
development and a circular economy.
(iv) Electrocatalysis holds great promise as analternative technology to conventional thermal catalysis
or traditional water electrolysis for the oxidation of
alcohols into carbonyl compounds. Nevertheless, current
research in this field still faces certain limitations. Firstly,
there is a lack of comprehensive investigation into therelationships between working electrode materials,
alcohol substrates, and electrogenerating intermediates.
This knowledge gap hampers our understanding ofreaction mechanisms and catalytic activities. Secondly,in electrocatalytic reactions, electrodes often struggle
to differentiate between various reactant molecules.
This can result in excessive oxidation/reduction of
products and redox reactions of solvent molecules,
thereby compromising reaction selectivity and productpurity. To overcome these challenges associated withhttps://doi.org/10.53964/id.2024001

single-electron reactions, a viable approach is tocombine photocatalysis with electrocatalysis, forming
a synergistic photocatalytic system. By leveraging
the potential of photocatalytic technology, it becomes
possible to achieve higher reaction selectivity andactivity in both homogeneous and heterogeneous
catalytic reactions, thus opening up new prospects inthis field.

Acknowledgements
This work was financially supported by the National
Natural Science Foundation of China (52002294) and
Knowledge Innovation Program of Wuhan-Shuguang
Project (2022010801020364).

Conflicts of Interest
The authors declared no conflict of interest.

Author Contribution
Liu J reviewed the literature and wrote the original
manuscript. Peng X provided ideas and revised thefinal manuscript.

Abbreviation List
C1 product, Formic acidC2 product, Glycolic acid
CV, Cyclic voltammetry
EG, Ethylene glycol
EGOR, Oxidation reaction of ethylene glycol
GA, Glycolic acid
HR-TEM, High-resolution transmission electron
microscopy
LSV, Linear sweep voltammetry
OER, Oxygen evolution reaction
PP, Polypropylene
RHE, Reversible hydrogen electrode
TPA/PTA, Terephthalic acid
PET/PETE, Polyethylene terephthalate

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Brief of Corresponding Author(s)Xiang Peng
He is a professor and PhD supervisor of Materials Science and Engineering at the Wuhan Instituteof Technology (WIT). He received his PhD in Physics and Materials Science from the City University of Hong Kong in 2017, where he laid the foundation for his future contributions to the field. Aftercompleting his doctoral studies, he continued to expand his expertise as a postdoctoral fellow at theCity University of Hong Kong from 2017 to 2018. His research focuses on the design of functional
nanomaterials and their application in energy storage and conversion. He has authored over 80
peer-reviewed papers, which have garnered significant recognition within the scientific community,
accumulating more than 6200 citations with an h index of 45. He currently serves as the associate editor of Innovation
Discovery as well as guest editor-in-chief and editorial board member of approximately 10 journals.

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