Synthesis and Characterization of Platinum-based Electrocatalyst for the Oxygen Reduction Reaction

PEM Fuel Cell, Oxygen reduction reaction, Alkaline metal, Intermetallic Pt alloy, Nanowirefirstly, the synthesis of a new active platinum alkaline earth alloy (PtMg) catalyst for the cathodic oxygen reduction reaction and secondly, the stabilization of the conventional PtCo alloy through morphology and phase maneuvering for high durability cathodic PEMFC catalyst. Recently, Sputter-cleaned polycrystalline alloy electrodes of platinum with alkaline earth metals (Ca, Sr, Ba) have been shown to exhibit over 5 fold enhanced electrocatalytic performance for oxygen reduction reaction (ORR) relative to polycrystalline platinum electrodes. Owing to the large oxophilicity of the alkaline metals, there exist challenges in scalable synthesis of such alloys similar to the challenges of platinum early transition metal alloys. Herein, a platinum-magnesium (Pt-Mg) alloy supported on high surface area carbon (Ketjen Black, EC600JD) is synthesized and found to display a 4-fold enhancement in performance and improved stability for the electrochemical reduction of oxygen as compared to a commercial state-of-the-art Pt/C catalyst. Secondly PtCo alloy electrocatalyst have been known to exhibit high catalytic performance for the oxygen reduction reaction (ORR). As such, it is of great importance for the industrial application of the fuel cell. Their durability is however unsatisfactory. Here, we report the synthesis and characterization of a remarkable one dimensional L10 ordered intermetallic PtCo alloy catalyst endowed with a high index faceted Pt-rich skin. These robust PtCo nanowires exhibit good Platinum utilization for the ORR displaying a liquid half-cell mass activity of 1.29 A/mgPt exceeding the 2020 targets of the DOE on Pt utilization for fuel cell applications and a higher power density relative to state of the art Pt/C as well as PtCo alloy nanoparticle in a single cell membrane electrode assembly (MEA). They also displayed excellent durability after 30,000 cycles of DOE recommended degradation test in the MEA. The excellent catalytic performance was attributed to the high index faceted Pt skin and the ligand effect arising from the Co underneath the Pt skin. The Pt-rich skin and a well ordered intermetallic core underlie the durability of the catalyst with the one-dimensional anisotropy offering a multipoint contact for anchoring platinum to carbon preventing detachment, migration and aggregation. This Masterc work demonstrates research into new catalytically active Pt alloy systeMaster (PtMg) as well as stabilization of well-known catalytically active but unstable Pt alloy systeMaster (PtCo) with application mainly in the fuel cell cathodic reaction (ORR). |본 논문에서는 두 가지 주제를 다룬다. 첫 번째는, 음극 산소 환원 반응을 위한 새로운 고활성의 백금 알칼리 토금속 합금(PtMg) 촉매의 합성이고, 두 번째는 고내구성 PEMFC 음극 촉매 개발을 위해 형태와 상 조절을 통한 기존의 PtCo 합금의 안정화이다. 최근에, 스퍼터링으로 청소된 다결정의 백금과 알칼린 토금속(칼슘, 스트론튬, 바륨)의 합금 전극은 산소환원반응(ORR)에서 다결정 백금 전극보다 5배 향상된 전기화학적 성능을 보였다. 알칼린 금속들의 높은 친산소성 때문에, 백금 앞 전이금속 합금 합성처럼 이런 합금들의 대량 합성에는 어려움이 있다. 본 학위 논문에서는, 고 비표면적 탄소(Ketjen black, EC600JD)로 지지된 백금-마그네슘(Pt-Mg) 합금을 합성했고, 이것은 최신 상용 Pt/C 촉매에 비해 산소의 전기화학적 환원에서 4배의 성능 증가와 향상된 안정성을 보였다. 다음으로 PtCo 합금 전기화학촉매는 산소환원반응(ORR)에서 높은 촉매 성능을 보인다고 알려져 있다. 이는 연료전지의 산업화에서 매우 중요한 점이다. 그러나 그런 촉매의 장기 안정성은 아직 부족하다. 본 논문에서는, 주목할만한 일차원 L10 형태로 정렬된 금속간 PtCo 합금 촉매의 합성과 특성 분석을 보고하였고, 해당 촉매는 고 밀러 지수 결정면의 백금 껍질을 가지고 있었다. 이 안정한 PtCo 나노와이어는 액체 반전지에서 1.29A/mgpt의 질량 활성을 보여주며 뛰어난 백금 활용성을 나타냈고, 이 질량 활성 값은 DOE의 연료 전지 활용을 위한 백금 활용성의 2020년 목표치를 넘어선 값이고 단전지 막 전극 집합체(MEA)에서 최근 상용 Pt/C 뿐만 아니라 PtCo 합금 나노입자와 비교했을 때 더 높은 출력 밀도를 보였다. 이 촉매는 또한 MEA에서 30,000 사이클의 DOE 성능 저하 시험 이후에도 탁월한 장기 안정성을 보였다. 이 뛰어난 촉매 성능은 고 밀러 지수 결정면의 백금 껍질과 그 백금 껍질 아래의 코발트로부터 발생한 리간드 효과에 기인한 것이다. 백금이 풍부한 껍질과 잘 정렬된 금속간 중심과 일차원 비등방성이 다중 접촉점을 제공하여 백금이 탄소에 정착되어 분리, 이동, 응집을 막아 촉매의 장기 안정성이 향상되었다. 본 학위 논문은 주로 연료전지 음극 반응(ORR)에서의 응용에서 새로운 촉매적으로 고활성인 백금 합금 시스템(PtMg) 뿐만 아니라 잘 알려진 촉매적으로 고활성이나 불안정한 백금 합금 시스템(PtCo)의 연구를 다루었다.This Masterc thesis presents two topicsprohibitionABSTRACT i List of AcronyMaster ii List of Table v List of Figures vi 1 INTRODUCTION - 1 - 1.1 Fuel Cell - 2 - 1.2 PEM Fuel Cell - 4 - 1.3 Component of the PEM Fuel Cell. - 5 - 1.3.1 Membrane - 5 - 1.3.2 Electrode - 7 - 1.3.3 Gas diffusion layer - 7 - 1.3.4 Bipolar plates - 8 - 1.4 Thermodynamics of the PEM Fuel Cell - 9 - 1.4.1 Fuel Cell Efficiency - 9 - 1.5 PEM Fuel Cell Reactions - 10 - 1.5.1 Oxygen Reduction Reaction - 10 - 1.5.2 Hydrogen Oxidation Reaction - 11 - 1.6 Electrocatalyst for the ORR - 11 - 1.6.1 Platinum Based ORR Electrocatalyst - 11 - 1.6.2 Non Platinum based ORR Electrocatalyst - 16 - 1.6.3 Stability of Platinum based ORR Electrocatalyst. - 17 - 2 PHYSICAL AND ELECTROCHEMICAL CHARACTERIZATION - 18 - 2.1.1 Physical Characterization - 18 - 2.1.2 Electrochemical Characterization - 18 - 2.1.3 Fuel Cell MEA test - 20 - 3 SYNTHESIS AND CHARACTERIZATION OF A HIGHLY STABLE NOVEL PLATINUM-MAGNESIUM ALLOY WITH ENHANCED CATALYTIC PERFORMANCE FOR THE ORR - 22 - 3.1 Introduction - 22 - 3.2 Experimental - 24 - 3.2.1 Chemicals - 25 - 3.2.2 Synthesis - 25 - 3.3 Results and Discussion - 26 - 3.4 Conclusions - 40 - 4 SYNTHESIS AND CHARACTERIZATION OF A DURABLE ONE-DIMENSIONAL INTERMETALLIC PtCo ALLOY FOR THE ORR - 42 - 4.1 Introduction - 42 - 4.2 Experimental - 44 - 4.2.1 Chemical - 44 - 4.2.2 Synthesis - 44 - 4.3 Results and Discussion - 45 - 4.4 Conclusions - 55 - 5 CONCLUSION AND OUTLOOK - 56 - 6 References - 59 - 요 약 문 - 64 -MasterdCollectio

Scrutinizing intrinsic oxygen reduction reaction activity of a Fe−N−C catalyst via scanning electrochemical cell microscopy

International audienceCarbon-based nanomaterials are renowned for their exceptional properties, making them propitious candidates for oxygen reduction reaction (ORR) electrocatalysis. However, their intrinsic activity is often challenging to investigate unambiguously with conventional methodologies due to the inherent complexities of such systems and the material itself. Zooming into the material and gaining electrochemical information with high resolution is a way to get rid of many experimental factors that influence the catalytic activity in macro-scale measurements. Herein, we employ nano-scale scanning electrochemical cell microscopy (SECCM) to investigate individual catalyst agglomerates with and without Nafion content. The intrinsic ORR activity of the catalyst was unravelled by using a unique approach of normalizing the data of all measured points by their distinctive electrochemical surface area (ECSA). When coupling with scanning electron microscopy (SEM), the structure and morphology of the catalytically active agglomerateswere visualize

Datasets for Reassessing the Intrinsic Hydrogen Evolution Reaction Activity of Platinum using Scanning Electrochemical Cell Microscopy published in Cell Reports Physical Science.

Data set for the publication '' Reassessing the Intrinsic Hydrogen Evolution Reaction Activity of Platinum using Scanning Electrochemical Cell Microscopy'' published in Cell Reports Physical Science

Insight into the Boosted Electrocatalytic Oxygen Evolution Performance of Highly Hydrophilic Nickel-Iron Hydroxide

Nickel-iron based materials are well-known catalysts for the oxygen evolution reaction (OER) and have been widely investigated. However, the synergy between these two components is still controversial. Herein, we report a facile immersion method for the synthesis of binder-free nickel-iron hydroxide loaded on Ni foam (NiFe-OH/NF) with superior hydrophilic property and high OER catalytic activity. The strong hydrophilic property of the binder-free NiFe-OH/NF electrode significantly enhances an effective contact between electrocatalyst and aqueous electrolyte and favors the bubble detachment from the electrode, facilitating the electron transfer and improving the OER activity. The hydrophilic NiFe-OH/NF can achieve a geometrical current density of 100 mA cm-1 at an extremely low overpotential (219 mV), along with a Tafel slope of 56 mV dec-1 and superior long-term stability at high current density in alkaline media, strongly indicating that the hydrophilicity plays an important role in improving the OER performance in the NiFe-OH/NF. Copyright © 2019 American Chemical Society.1

Positive self-reconstruction in an FeNiMo phosphide electrocatalyst for enhanced overall water splitting

Searching for low-cost and highly active bifunctional electrocatalysts toward hydrogen/oxygen evolution reactions is a grand challenge for water splitting hydrogen production. Herein, we prepare a trimetallic nickel, iron, and molybdenum phosphide (FeNiMoP) grown on nickel foam (NF)viaa facile two-step process and employ it as a bifunctional electrocatalyst for full water splitting. In virtue of the superior hydrogen/oxygen evolution activity, the cell with the bifunctional FeNiMoP as both anode and cathode exhibits an initial low cell voltage of 1.50 V at a current density of 10 mA cm−2in 1.0 M KOH electrolyte solution. Impressively, the full cell voltage decreases to 1.44 V through favorable self-reconstruction on both the anode and cathode during the electrocatalytic overall water splitting process. On the anode side, the FeNiMoP is transformed into FeNiOOH while Mo and P elements are dissolved into the electrolyte. Such transformation leads to a continuously increasing active surface area, and the dissolved Mo forms MoO42−in the electrolyte which improves the OER performance. On the cathode side, the dissolution and re-deposition of Mo oxides on the surface of the electrode greatly increase the active surface sites towards the electrolytes, and the surface absorbed Mo oxides play key roles, leading to a positive effect on HER performance. The new synthesis strategy, taking advantage of favorable structural self-reconstruction in the catalysts can be extended to other catalytic systems. © The Royal Society of Chemistry 2021.1

Tailor-Made Pt Catalysts with Improved Oxygen Reduction Reaction Stability/Durability

With recent technological advances, the demand for renewable energy is ever growing. Polymer electrolyte membrane fuel cells (PEMFCs) have shown great promise in subduing various environmental and energy issues. However, the use of a platinum (Pt) electrocatalyst on both cathode and anode sides of the PEMFCs has caused economical and sustainability hurdles in the commercialization of such devices. To alleviate these problems with Pt catalysts, various avenues have been researched and used. In the present Review, we have tried to look into the problems associated with the stability of the Pt-based electrocatalysts. Here, the scope of the current Review is categorized into three issues regarding the stability of Pt electrocatalysts: shape-controlled structure, alloy and core-shell structure, and supporting materials for Pt-based electrocatalysts. Major factors influencing the stability of the Pt-based electrocatalysts have been discussed, and various parameters needed for increasing the stability are also considered. © 2019 American Chemical Society.1

Strained Pt(221) Facet in a PtCo@Pt-Rich Catalyst Boosts Oxygen Reduction and Hydrogen Evolution Activity

Over the last years, the development of highly active and durable Pt-based electrocatalysts has been identified as the main target for a large-scale industrial application of fuel cells. In this work, we make a significant step ahead in this direction by preparing a high-performance electrocatalyst and suggesting new structure-activity design concepts which could shape the future of oxygen reduction reaction (ORR) catalyst design. For this, we present a new one-dimensional nanowire catalyst consisting of a L1(0) ordered intermetallic PtCo alloy core and compressively strained high-index facets in the Pt-rich shell. We find the nanoscale PtCo catalyst to provide an excellent turnover for the ORR and hydrogen evolution reaction (HER), which we explain from high-resolution transmission electron microscopy and density functional theory calculations to be due to the high ratio of Pt(221) facets. These facets include highly active ORR and HER sites surprisingly on the terraces which are activated by a combination of sub-surface Co-induced high Miller index-related strain and oxygen coverage on the step sites. The low dimensionality of the catalyst provides a cost-efficient use of Pt. In addition, the high catalytic activity and durability are found during both half-cell and proton exchange membrane fuel cell (PEMFC) operations for both ORR and HER. We believe the revealed design concepts for generating active sites on the Pt-based catalyst can open up a new pathway toward the development of high-performance cathode catalysts for PEMFCs and other catalytic systems. © 2022 American Chemical Society. All rights reserved.FALS

Fast Li‐ion storage and dynamics in TiO2 nanoparticle clusters probed by smart scanning electrochemical cell microscopy

Anatase TiO2 is a promising material for Li-ion (Li+) batteries with fast charging capability. However, Li+ (de)intercalation dynamics in TiO2 remain elusive and reported diffusivities span many orders of magnitude. Here, we develop a smart protocol for scanning electroche­mical cell microscopy (SECCM) with in situ optical microscopy (OM) to enable the high-throughput charge/discharge analysis of single TiO2 nanoparticle clusters. Directly probing active nanoparticles revealed that TiO2 with a size of ~50 nm can store over 30% of the theoretical capacity at an extremely fast charge/discharge rate of ~100 C. This finding of fast Li+ storage in TiO2 particles strengthens its potential for fast-charging batteries. More generally, smart SECCM-OM should find wide applications for high-throughput electrochemical screening of nanostructured materials

New PtMg Alloy with Durable Electrocatalytic Performance for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell

Polycrystalline alloy electrodes of Pt with alkaline earth metals (Ca, Sr, and Ba) have been shown to exhibit enhanced electrocatalytic performance for oxygen reduction reaction (ORR) relative to Pt electrodes. The large oxophilicity of the alkaline earth metals makes it challenging to synthesize such alloys. Here, we synthesize a carbon-supported platinum-magnesium (PtMg) alloy with enhanced catalytic activity and durability for the ORR in both a half-cell and single cell when compared to the state-of-the-art Pt/C catalyst. Employing metallic Mg powder as a precursor can overcome the large oxophilicity of Mg and induce alloying of Mg with Pt, whereas conventional Mg salts do not form an alloy. Density functional theory calculations elucidate the origin of the enhanced catalytic activity and durability. Complementary physical and electrochemical analyses also evidence them in this work. This material holds great application potential and will contribute to elucidation of the effects of alloying Pt with electropositive metals. © 2020 American Chemical Society.1

Scrutinizing intrinsic oxygen reduction reaction activity of a Fe−N−C catalyst via scanning electrochemical cell microscopy

Carbon-based nanomaterials are renowned for their exceptional properties, making them propitious candidates for oxygen reduction reaction (ORR) electrocatalysis. However, their intrinsic activity is often challenging to investigate unambiguously with conventional methodologies due to the inherent complexities of such systems and the material itself. Zooming into the material and gaining electrochemical information with high resolution is a way to get rid of many experimental factors that influence the catalytic activity in macro-scale measurements. Herein, we employ nano-scale scanning electrochemical cell microscopy (SECCM) to investigate individual catalyst agglomerates with and without Nafion content. The intrinsic ORR activity of the catalyst was unravelled by using a unique approach of normalizing the data of all measured points by their distinctive electrochemical surface area (ECSA). When coupling with scanning electron microscopy (SEM), the structure and morphology of the catalytically active agglomerates were visualized