Functionalization of carbons for Pt electrocatalyst in PEMFC

One of the limitations of conventional carbon-supported Pt electrocatalyst in Proton Exchange Membrane Fuel cell (PEMFC) is the carbon corrosion during start-up and shut-down of a fuel cell. The present work investigates the stability of three different carbon blacks and their functionalized forms as supports for Pt electrocatalysts. Acetylene black (AB) as a low surface area carbon shows a higher degree of graphitization and effective functionalization than Vulcan carbon and Ketjan black. Electrochemical tests on corrosion studies show that the AB and its functionalized form (f-AB) as support for Pt electrocatalyst exhibits good electrochemical activity with an ECSA of 52 m²g^-1 and 78 m²g^-1 and excellent corrosion resistance with minimum ECSA loss of 6% and 16% for Pt/AB and Pt/f-AB, respectively, satisfying the DoE target (<40% ECSA loss.) This makes the Pt/f-AB a promising durable electrocatalyst for PEMFC with improved activity and durability.     

Medulla stachyuri-derived iron and nitrogen co- doped 2D porous carbon-flakes for highly efficient oxygen reduction electrocatalysis and supercapacitors

Iron and nitrogen co-doped two-dimensional (2D) porous carbon-flakes have been fabricated by using foam-like Medulla stachyuri (MS, the stem pith of tetrapanax papyrifer) as both carbon precursor and template and ammonium ferric citrate as iron and nitrogen precursor. The ammonium ferric citrate-impregnated foams are subsequently converted into iron and nitrogen co-doped 2D porous carbon-flakes by pyrolysis at high temperature in an inert atmosphere. The porous carbon-flakes fabricated at 900 °C (MS-Fe-900) possess high surface area (1140.9 m² g⁻¹) and effective Fe/N co-doping (0.22 at.% Fe and 2.02 at.% N). In comparison with Pt/C, MS-Fe-900 exhibits superior ORR activity (E₀ = 968 mV; E_1/2 = 830 mV vs RHE), preferable methanol/CO tolerance and better stability. Furthermore, the MS-Fe-900-based electrode presents high-rate performance (80.1% capacitance retention from 1 to 100 A g⁻¹), and good cycling stability for over 10000 cycles in 6 M KOH electrolyte. This work takes full advantage of the unique structure of biomass and provides a feasible approach to develop cost-efficient and high performance activated carbon materials for ORR electrocatalysis and supercapacitors.     

Walnut shell-derived hierarchical porous carbon with high performances for electrocatalytic hydrogen evolution and symmetry supercapacitors

Walnut Shell-derived hierarchical porous carbon has been successfully synthesized by the efficient KOH activation process. The hierarchical porous carbon material activated at 600 °C, has the specific micropore area of 1037.31 m² g⁻¹ and micropore volume of 0.51 cm³ g⁻¹, which leads to have electrochemical performances of the hydrogen evolution reaction (HER) and supercapacitors. Specifically, as the hydrogen evolution reaction electrocatalyst, the walnut shell-derived carbon material activated at 600 °C exhibits a lower onset potential of 6.00 mV, a smaller Tafel slope of 69.76 mV dec⁻¹ and outstanding stability above long-term cycling. As a supercapacitor electrode material, the sample possesses specific capacitance of 262.74 F g⁻¹ at 0.5 A g⁻¹, the remarkable rate capability of 224.60 F g⁻¹ at even 10 A g⁻¹ and good long-term stability. A symmetric supercapacitor shows the highly energy density of 7.97 Wh kg⁻¹ at a power density of 180.80 W kg⁻¹. This novel and low-cost biomass material is very promising for the electrocatalytic water splitting and supercapacitors.     

Bio-derived nanoporous activated carbon sheets as electrocatalyst for enhanced electrochemical water splitting

Designing highly efficient and durable metal-free electro-catalysts replacing the precious (non)noble metals is crucial to the future hydrogen economy and various renewable energy conversion and storage devices. Herein, we report an efficient low-cost nanoporous activated carbon sheets (NACS) with hierarchical pore architecture from Indian Ooty Varkey (IOV) food waste for oxygen evolution (OER) and hydrogen evolution reactions (HER) by following “waste to wealth creation” strategy. Characterization of NACS carbo-catalyst reveals the presence of pyridinic-nitrogen inherited by self-doping of N from the biomass with high BET surface area (1478.0 m² g^-1). As an electrocatalyst in alkaline medium, it exhibits low-onset potential (1.36 V vs. RHE), an overpotential (η₁₀) of 0.34 V at 10.0 mA cm⁻² with a small Tafel value (43 mV dec⁻¹), and good stability towards OER compared to Pt or Ir commercial catalysts. Tested as HER catalyst, it displays an impressive HER activity with a low-onset potential of −0.085 V (vs. RHE), and overpotential (η₁₀) of 0.38 V at 10.0 mA cm⁻² with a small Tafel slope of 85 mV dec⁻¹.     

Platinum nanoparticles decorated Nb2CTx MXene as an efficient dual functional catalyst for hydrogen evolution and oxygen reduction reaction

Here, a dual functional Nb₂CT_x@Pt nanocomposite has been synthesized by in situ reduction method. The Pt loading in the composite has been optimized to get minimum overpotential (141 mV at 10 mA/cm²) for hydrogen evolution reaction (HER) along with a promising Tafel slope of 46.3 mV/dec, while Pt/C shows an overpotential and Tafel slope of 104 mV and 32.4 mV/dec, respectively. The Pt mass activity for Nb₂CT_x@Pt3.8 composite at 100 mV overpotential was 3.44 A g^?1 while the Pt mass activity for conventional Pt/C was 0.7 A g^?1, which shows that the activity of Nb₂CT_x@Pt3.8 composite is approximately 5 times higher than Pt/C. In addition, the catalyst was found to be stable for continuous 500 cycles without any binder molecules. The oxygen reduction reaction (ORR) capability of the material was also evaluated and found that the catalyst exhibited a current density of ?4.28 mA/cm² in the diffusion limiting region in comparison with the current density of ?5.82 mA/cm² for Pt/C at 2600 revolutions per minute (RPM). The Pt mass activity of Nb₂CT_x@Pt3.8 composite for ORR is approximately 10 times higher than Pt/C. The Nb₂CT_x@Pt3.8 composite was able to reduce O₂ completely using the 4-electron pathway with very little peroxide production. From these results, the dual functionality of the Nb₂CT_x@Pt3.8 composite for both HER and ORR has been established.     

Nitrogen doped mesoporous carbon supported Pt electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Nitrogen doped mesoporous carbons are employed as supports for efficient electrocatalysts for oxygen reduction reaction. Heteroatom doped carbons favour the adsorption and reduction of molecular oxygen on Pt sites. In the present work, nitrogen doped mesoporous carbons (NMCs) with variable nitrogen content were synthesized via colloidal silica assisted sol-gel process with Ludox-AS40 (40 wt% SiO₂) as hard template using melamine and phenol as nitrogen and carbon precursors, respectively. The NMC were used as supports to prepare Pt/NMC electrocatalysts. The physicochemical properties of these materials were studied by SEM, TEM, XRD, BET, TGA, Raman, XPS and FTIR. The surface areas of 11 wt% (NMC-1) and 6 wt% (NMC-2) nitrogen doped mesoporous carbons are 609 m² g^?1 and 736 m² g^?1, respectively. The estimated electrochemical surface areas for Pt/NMC-1 and Pt/NMC-2 are 73 m² g^?1 and 59 m² g^?1, respectively. It is found that Pt/NMC-1 has higher ORR activity with higher limiting current and 44 mV positive onset potential shift compared to Pt/NMC-2. Further, the fuel cell assembled with Pt/NMC-1 as cathode catalyst delivered 1.8 times higher power density than Pt/NMC-2. It is proposed that higher nitrogen content and large pyridinic nitrogen sites present in NMC-1 support are responsible for higher ORR activity of Pt/NMC-1 and high power density of the fuel cell using Pt/NMC-1 cathode electrocatalyst. The carbon support material with high pyridinic content promotes the Pt dispersion with particle size less than 2 nm.     

Chemically and thermally reduced graphene oxide supported Pt catalysts prepared by supercritical deposition

Reduced graphene oxide (RGO) is used in many energy applications, especially in Polymer Electrolyte Membrane (PEM) fuel cells, as carbon sourced catalyst support materials. In this study, thermally (T-RGO) and chemically (C-RGO) reduced GO support materials were synthesized for utilization in PEM fuel cells. Pt catalysts were synthesized using supercritical carbon dioxide (SCCO₂) deposition technique over synthesized support materials. Physical (BET, SEM-EDX, FTIR, RAMAN, XRD, TEM, ICP-MS and optical tensiometer) and electrochemical (CV, PEM fuel cell test) characterizations of synthesized support materials and corresponding Pt catalysts were performed. The differences between the structures of thermally and chemically reduced graphene oxide supports and their Pt catalysts were investigated. The ECSA values of the Pt/T-RGO and Pt/C-RGO catalysts are 19.86 m² g^?1 and 6.31 m² g^?1, respectively. The current and power density values of the Pt/T-RGO and Pt/C-RGO catalysts at 0.6 V are 84 mA cm^?2, 80 mA cm^?2 and 50 mW cm^?2, 45 mW cm^?2, respectively. Pt/T-RGO and Pt/C-RGO catalysts showed similar trend in PEMFC environment.     

Preparation and characterization of activated carbon from rubber-seed shell by physical activation with steam

The use of rubber-seed shell as a raw material for the production of activated carbon with physical activation was investigated. The produced activated carbons were characterized by Nitrogen adsorption isotherms, Scanning electron microscope, Thermo-gravimetric and Differential scanning calorimetric in order to understand the rubber-seed shell activated carbon. The results showed that rubber-seed shell is a good precursor for activated carbon. The optimal activation condition is: temperature 880 °C, steam flow 6 kg h^?1, residence time 60 min. Characteristics of activated carbon with a high yield (30.5%) are: specific surface area (S_BET) 948 m² g^?1, total volume 0.988 m³ kg^?1, iodine number of adsorbent (q_iodine) 1.326 g g^?1, amount of methylene blue adsorption of adsorbent (q_mb) 265 mg g^?1, hardness 94.7%. It is demonstrated that rubber-seed shell is an attractive source of raw material for producing high capacity activated carbon by physical activation with steam.     

A novel hard-template method for fabricating tofu-gel based N self-doped porous carbon as stable and cost-efficient electrocatalyst in microbial fuel cell

A novel hard-template method to fabricate tofu-gel based N self-doped porous carbon (NC-X) as excellent oxygen reduction reaction (ORR) electrocatalyst, in which CaCO₃ is in-situ formed from flocculant and then served as hard-template. The as-prepared NC-3 delivers a high specific surface area (609.10 m² g⁻¹), pore volume (0.68 cm³ g⁻¹) and nitrogen content (7.20 at. %). Reasonably, NC-3 possesses more positive on-set potential (0.132 V vs. Ag/AgCl) and half-wave potential (−0.041 V vs. Ag/AgCl). Furthermore, the output voltage and maximum power density of NC-3 coated as cathode in microbial fuel cell (MFC) are enhanced to 533.65 ± 12.09 mV and 471.82 ± 15.39 mW m⁻², respectively. Noted that NC-3 (2.15 × 10⁻³ $ g⁻¹) also shows nice long-term stability and anti-poisoning to methanol, and is nearly 100,000 times cheaper than commercial Pt/C (20 wt %, 220.04 $ g⁻¹). Therefore, NC-3 should be a very promising ORR catalyst in the application of MFC.     

Electrochemical fabrication of long-term stable Pt-loaded PEDOT/graphene composites for ethanol electrooxidation

Layered electrochemically reduced graphene oxide (ER-GO) sheets incorporated with poly(3,4-ethylenedioxythiophene) (PEDOT) have been fabricated as an efficient support for Pt nanoparticles on a glassy carbon (GC) electrode. The as-prepared Pt-loaded PEDOT/ER-GO composite electrode exhibits not only the high mass peak current density (390 A g⁻¹) but also the good long-term catalytic stability toward the ethanol electrooxidation. The Pt/PEDOT/ER-GO also shows stronger tolerance to poisoning species compared with the commercial JM 20% Pt/C electrode. The high electrocatalytic activity of Pt/PEDOT/ER-GO is mainly described to the good electrochemical activity of PEDOT/ER-GO composites and the well-dispersed Pt nanoparticles resulting in the large electrochemical active surface area of Pt (47.1 m² g⁻¹).     

An effective electrocatalyst based on platinum nanoparticles supported with graphene nanoplatelets and carbon black hybrid for PEM fuel cells

A facile synthesis at room temperature and at solid-state directly on the support yielded small, homogeneous and well-dispersed Pt nanoparticles (NPs) on CB-carbon black, GNP-graphene nanoplatelets, and CB-GNP-50:50 hybrid support. Synthesized Pt/CB, Pt/GNP and Pt/CB:GNP NPs were used as electrocatalysts for polymer electrolyte membrane fuel cell (PEMFC) reactions. HRTEM results displayed very small, homogeneous and well-dispersed NPs with 1.7, 2.0 and 4.2 nm mean-diameters for the Pt/CB-GNP, Pt/GNP and Pt/CB electrocatalysts, respectively. Electrocatalysts were also characterized by RAMAN, XRD, BET and CV techniques. ECSA values indicated better activity for graphene-based supports with 19 m² g⁻¹_Pt for Pt/GNP and 55 m² g⁻¹_Pt for Pt/CB-GNP compared to 10 m² g⁻¹_Pt for Pt/CB. Oxygen reduction reaction (ORR) studies and fuel cell tests were in parallel with these results where highest maximum power density of 377 mW cm⁻² was achieved with Pt/CB-GNP hybrid electrocatalyst. Both fuel cell and ORR studies for Pt/CB-GNP indicated better dispersion of NPs on the support and efficient fuel cell performance that is believed to be due to the prevention of restacking of GNP by CB. To the best of our knowledge, Pt/GNP and Pt/CB-GNP electrocatalysts are the first in literature to be synthesized with the organometallic mild synthesis method using Pt(dba)₃ precursor for the PEMFC applications.     

Waste wine mash-derived doped carbon materials as an efficient electrocatalyst for oxygen reduction reaction

Oxygen reduction reaction (ORR) is a core reaction of fuel cell and metal-air cell. In recent years, it has been a hot topic to study non-precious metal catalysts for ORR. Herein, we have used waste wine mash-derived carbon, melamine and ferric chloride to prepare a Fe- and N- co-doped carbon catalyst. The specific surface area of the catalyst is up to 1066.6 m² g⁻¹. And its wave potential is 15 mV higher than that of commercial Pt/C catalyst. The ORR on our catalyst followed a four-electron pathway; and it has high stability and high impressive immunity to methanol. After continuous oxygen reduction of 30,000s, the retention rate is 90%.     

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H₂PtCl₆ as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m² g⁻¹) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g⁻¹) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g⁻¹) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g⁻¹). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.     

Self-doped Sargassum spp. derived biocarbon as electrocatalysts for ORR in alkaline media

In this work, high surface area N-doped carbon synthesis from Sargassum spp. is reported as a low cost alternative for electrocatalysts production for the oxygen reduction reaction (ORR). First, Sargassum spp. was activated with potassium hydroxide (SKPH) and then doped with hydrazine (SKPHD). As a result of the activation process, SKPH obtained a high surface area (2289 m² g⁻¹), 0.16% nitrogen and 2.63% sulfur content; it also showed four-electron-transfer mechanism when tested as electrocatalyst in alkaline medium. Besides, SKPHD presented 3.60% nitrogen content in the bulk and higher ORR activity (0.838 V onset potential vs. RHE and 4.59 mA cm⁻² current density) very close to 20% Pt/C (5.25 mA cm⁻²). Results indicate that using seaweeds as a synthesis precursor is an alternative for the Sargassum spp. disposal in the Caribbean due to its high availability and efficiency towards ORR.     

Lattice-strained Pt nanoparticles anchored on petroleum vacuum residue derived N-doped porous carbon as highly active and durable cathode catalysts for PEMFCs

High cost and poor durability of Pt-based cathode catalysts for oxygen reduction reaction (ORR) severely hamper the popularization of proton exchange membrane fuel cells (PEMFCs). Tailoring carbon support is one of effective strategies for improving the performance of Pt-based catalysts. Herein, petroleum vacuum residue was used as carbon source, and nitrogen-doped porous carbon (N-PPC) was synthesized using a simple template-assisted and secondary calcination method. Small Pt nanoparticles (Pt NPs) with an average particles size of 1.8 nm were in-situ prepared and spread evenly on the N-PPC. Interestingly, the lattice compression (1.08%) of Pt NPs on the N-PPC (Pt/N-PPC) was clearly observed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which was also verified by the shift of (111) crystal plane of Pt on N-PPC to higher angles. The X-ray photoelectron spectroscopy (XPS) results suggest that the N-PPC support had a strong effect on anchoring Pt NPs and endowing surface Pt NPs with lowered d band center. Thus, the Pt/N-PPC as a catalyst simultaneously boosted the ORR activity and durability. The specific activity (SA) and mass activity (MA) of the Pt/N-PPC at 0.9 V reached 0.83 mA cm⁻² and 0.37 A mg_Pt⁻¹, respectively, much higher than those of the commercial Pt/C (0.21 mA cm⁻² and 0.11 A mg_Pt⁻¹) in 0.1 M HClO₄. The half-wave potential (E_1/2) of Pt/N-PPC exhibited only a minimal negative shift of 7 mV after 30,000 accelerated durability tests (ADT) cycles. More importantly, an H₂–O₂ fuel cell with a Pt/N-PPC cathode achieved a power density of 866 mW cm⁻², demonstrating that the prepared catalyst has a promising application potential in working environment of PEMFCs.     

Promising nature-based nitrogen-doped porous carbon nanomaterial derived from borassus flabellifer male inflorescence as superior metal-free electrocatalyst for oxygen reduction reaction

In this present study, novel hierarchical nitrogen-doped porous carbon for use as a metal-free oxygen reduction reaction (ORR) electrocatalyst is derived from borassus flabellifer male inflorescences by calcining at 1000 °C in an inert atmosphere using metal hydroxides as activating agent and melamine as nitrogen doping agent. The BET surface areas of the lithium-ion (Li-ion), potassium-ion (K-ion) and calcium-ion (Ca-ion) activated carbon are observed to be 824.02, 810.88 and 602.88 m² g^-1 respectively. Another interesting fact is that the total surface energy calculated by wicking method (73.2 mJ/m²), is found to be higher for Li-ion activated carbons. Among the prepared nitrogen-doped porous carbon, Li-ion activated system, showed an outstanding performance in ORR reaction in alkaline medium, thanks to its high surface area and notable surface activity. An incontrovertible of note that ORR half-wave potential of Li-ion activated nitrogen-doped carbon (0.90 V) is relatively higher in comparison to the commercial 20 wt % Pt/C catalyst (0.86 V). Inspite of overwhelming performance, the ORR reaction followed the preferred 4- electron transfer mechanism involving in the direct reduction pathway in all activated carbons. The ORR performance is also noticeably better and comparable to the best results in the literature based on biomass derived carbon catalysts.     

Preparation and characterization of platinum/iron contained hydroxyapatite/carbon black composites

In this report, calcium ions in the porous hydroxyapatite (HAp) microspheres are partially exchanged with ferrous ions to form iron contained hydroxyapatite (FeHAp) on which Pt ions in H₂PtCl₆ solution are reduced to form Pt/FeHAp catalyst and finally mixed with carbon blacks to derive Pt/FeHAp/C catalysts. They exhibit the characteristics of Pt (1 1 0) facet with a sharp desorption peak at −0.109 V (vs. Ag/AgCl), the electrochemical surface area (ECSA) ranging from 73 to 224 m² g⁻¹ with little CO poisoning effect on Pt, and the mass activity ranging from 6.88 to 28.99 A g_Pt⁻¹ in methanol oxidation reaction (MOR) at 0.4 V (vs. Ag/AgCl). Besides, Pt/FeHAp reveals the lower onset potential in CO-stripping than Pt/C. These better performances of Pt/FeHAp/C catalysts, compared with Pt/C, are also related to the Pt (1 1 0) facet, the content of Fe, and the coexistence of Pt⁰ and Pt²⁺ in Pt/FeHAp.     

Tungsten carbide modified high surface area carbon as fuel cell catalyst support

Phase pure WC nanoparticles were synthesized on high surface area carbon black (800 m² g⁻¹) by a temperature programmed reaction (TPR) method. The particle size of WC can be controlled under 30 nm with a relatively high coverage on the carbon surface. The electrochemical testing results demonstrated that the corrosion resistance of carbon black was improved by 2-fold with a surface modification by phase pure WC particles. However, the WC itself showed some dissolution under potential cycling. Based on the X-ray diffraction (XRD) and inductively coupled plasma (ICP) analysis, most of the WC on the surface was lost or transformed to oxides after 5000 potential cycles in the potential range of 0.65-1.2 V. The Pt catalyst supported on WC/C showed a slightly better ORR activity than that of Pt/C, with the Pt activity loss rate for Pt/WC/C being slightly slower compared to that of Pt/C. The performance and decay rate of Pt/WC/C were also evaluated in a fuel cell.     

Evaluation of the corrosion of Sb-doped SnO2 supports for electrolysis systems

The corrosion behaviour and electrochemical stability of two different electrocatalyst supports based on Sb-doped SnO₂ (ATO) were evaluated in an acidic medium over a wide potential range (0–1.8 V vs. NHE). The results were compared with those from a commercial Vulcan carbon XC-72 (254 m² g⁻¹) support. ATO (85 m² g⁻¹) and modified-ATO (216 m² g⁻¹) were synthesized by the sol–gel method and were then characterized by XRD, BET and TEM. The modification of the ATO consisted of adding dodecylamine as a surfactant to generate a surface area similar to that of Vulcan carbon. The electrochemical characterization conditions were chosen to match the operating conditions of a proton exchange membrane fuel cell (PEMFC) and a solid polymer electrolyser (SPE), where the oxygen-evolution reaction takes place at a potential near 1.6 V with respect to normal hydrogen electrode (NHE). The results show good chemical stability when the ATO and the modified-ATO are subjected to these conditions, whereas Vulcan carbon corrodes easily. This indicates that Sb-doped SnO₂ is a good candidate for electrocatalyst supports for energy-conversion systems such as electrolysers and unified regenerative fuel cells.     

Self-assembled mesoporous carbon sensitized with ceria nanoparticles as durable catalyst support for PEM fuel cell

Mesocarbon-ceria nanocomposite is proposed for developing highly durable catalyst for the application in fuel cells. Ordered arrays of the mesoporous channels with d spacing of ∼8 nm and wall thickness of ∼3 nm are fabricated through a self-assembly route between the phenolic oligomers and PEO-containing P123 block polymer combined with self-assembly of CeOH₂⁺ and the surfactant. As a result, the Pt-mesocarbon-ceria presents a high electrochemically active surface of 105 m²/g_Pt. It is also found that ceria has an appreciable influence on the performance of the fuel cell at low humidity due to the water retention of ceria nanoparticles. At 75 RH% humidity of 65 °C, single cell assembled with Pt-mesocarbon-ceria has performance better than that of the conventional Pt/C catalyst. The Pt-mesocarbon-ceria displays high resistance to corrosion because of radical scavenges of ceria. Under long period operation at open circuit voltage (OCV), the voltage of the fuel cell assembled with Pt-mesocarbon-ceria has a slight decay rate of 9.5 μV/min, in comparison to 28.5 μV/min of conventional Pt/C. After an OCV accelerated degradation of 2000 min, the electrochemically active surface of Pt-mesocarbon-ceria is 45%, much lower than 70% of Pt/C catalyst.