The well-known limitation of alkaline
fuel cells is the slack kinetics
of the cathodic half-cell reaction, the oxygen reduction reaction
(ORR). Platinum, being the most active ORR catalyst, is still facing
challenges due to its corrosive nature and sluggish kinetics. Many
novel approaches for substituting Pt have been reported, which suffer
from stability issues even after mighty modifications. Designing an
extremely stable, but unexplored ordered intermetallic structure,
Pd2Ge, and tuning the electronic environment of the active
sites by site-selective Pt substitution to overcome the hurdle of
alkaline ORR is the main motive of this paper. The substitution of
platinum atoms at a specific Pd position leads to Pt0.2Pd1.8Ge demonstrating a half-wave potential (E
1/2) of 0.95 V vs RHE, which outperforms the state-of-the-art
catalyst 20% Pt/C. The mass activity (MA) of Pt0.2Pd1.8Ge is 320 mA/mgPt, which is almost 3.2 times
better than that of Pt/C. E
1/2 and MA
remained unaltered even after 50,000 accelerated degradation test
(ADT) cycles, which makes it a promising stable catalyst with its
activity better than that of the state-of-the-art Pt/C. The undesired
2e– transfer ORR forming hydrogen peroxide (H2O2) is diminished in Pt0.2Pd1.8Ge as visible from the rotating ring-disk electrode (RRDE) experiment,
spectroscopically visualized by in situ Fourier transform infrared
(FTIR) spectroscopy and supported by computational studies. The effect
of Pt substitution on Pd has been properly manifested by X-ray absorption
spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The
swinging of the oxidation state of atomic sites of Pt0.2Pd1.8Ge during the reaction is probed by in situ XAS,
which efficiently enhances 4e– transfer, producing
an extremely low percentage of H2O2.
Electrochemical CO2 reduction reaction (eCO2RR) is performed on two intermetallic compounds formed by copper and gallium metals (CuGa2 and Cu9Ga4). Among them, CuGa2 selectively converts CO2 to methanol with remarkable Faradaic efficiency of 77.26% at an extremely low potential of −0.3 V vs RHE. The high performance of CuGa2 compared to Cu9Ga4 is driven by its unique 2D structure, which retains surface and subsurface oxide species (Ga2O3) even in the reduction atmosphere. The Ga2O3 species is mapped by X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption fine structure (XAFS) techniques and electrochemical measurements. The eCO2RR selectivity to methanol are decreased at higher potential due to the lattice expansion caused by the reduction of the Ga2O3, which is probed by in situ XAFS, quasi in situ powder X‐ray diffraction, and ex situ XPS measurements. The mechanism of the formation of methanol is visualized by in situ infrared (IR) spectroscopy and the source of the carbon of methanol at the molecular level is confirmed from the isotope‐labeling experiments in presence of 13CO2. Finally, to minimize the mass transport limitations and improve the overall eCO2RR performance, a poly(tetrafluoroethylene)‐based gas diffusion electrode is used in the flow cell configuration.
Electrocatalytic CO2 reduction (eCO2RR) is one of the avenues with most potential toward achieving sustainable energy economy and global climate change targets by harvesting renewable energy into value‐added fuels and chemicals. From an industrial standpoint, eCO2RR provides specific advantages over thermochemical and photochemical pathways in terms of much broader product scope, high product specificity, and easy adaptability to the renewable electricity infrastructure. However, unlike water electrolyzers, the lack of suitable cathode materials for eCO2RR impedes its commercialization due to material design challenges. The current state‐of‐the‐art catalysts in eCO2RR suffer largely from low reaction rates, insufficient C2+ product selectivity, high overpotentials, and industrial‐scale stability. Overcoming the scientific and applied technical hurdles for commercial realization demands a holistic integration of catalytic designs, deep mechanistic understanding, and efficient process engineering. Special emphasis on mechanistic understanding and performance outcome is sought to guide the future design of eCO2RR catalysts that can play a significant role in closing the anthropogenic carbon loop. This article provides an integrative approach to understand principles of robust eCO2RR catalyst design superimposed with underlying mechanistic projections which strongly depend on experimental conditions viz. choice of electrolyte, reactor and membrane design, pH of the solvent, and partial pressure of the CO2.
Electrochemical
reduction of CO2 into valuable fuels
and chemicals is a promising route of replacing fossil fuels by reducing
CO2 emissions and minimizing its adverse effects on the
climate. Tremendous efforts have been carried out for designing efficient
catalyst materials to selectively produce the desired product in high
yield from CO2 by the electrochemical process. In this
work, a strategy is reported to enhance the electrochemical CO2 reduction reaction (ECO2RR) by constructing an
interface between a metal-based alloy (PdIn) nanoparticle and an oxide
(In2O3), which was synthesized by a facile solution
method. The oxide-derived PdIn surface has shown excellent eCO2RR activity and enhanced CO selectivity with a Faradaic efficiency
(FE) of 92.13% at −0.9 V (vs RHE). On the other hand, surface
PdO formation due to charge transfer on the bare PdIn alloy reduces
the CO2RR activity. With the support of in situ (EXAFS
and IR) and ex situ (XPS, Raman) spectroscopic techniques, the optimum
presence of the Pd–In–O interface has been identified
as a crucial parameter for enhancing eCO2RR toward CO in
a reducing atmosphere. The influence of eCO2RR duration
is reported to affect the overall performance by switching the product
selectivity from H2 (from water reduction) to CO (from
eCO2RR) on the oxide-derived alloy surface. This work also
succeeded in the multifold enhancement of the current density by employing
the gas diffusion electrode (GDE) and optimizing its process parameters
in a flow cell configuration.
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