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Carbon supported Pt catalyst materials were synthesized from waste tire derived carbon by two different methods (microwave and refluxing). Catalysts and carbons were physically (XRD, N2 sorption analysis, TGA) and electrochemically characterized (RDE, CV, PEMFC single cell measurements). The RDE measurements were performed in 0.1 M HClO4 solution. For PEMFC single cell measurements, membrane-electrode assembly systems (MEAs) were prepared from catalyst materials by using different methods of coating the cathode layer and additional treatments. Catalysts were sprayed onto the membrane or GDL. In addition, MEAs were prepared where the catalyst was pipetted into GDL in several drops. Some of the MEAs were additionally treated with extra layer of Nafion and hot-pressed. The highest power density (0.42 W cm−2) was achieved with the MEA where the Pt catalyst synthesized via refluxing method was coated on the GDL with multiple drops and additional treatments were applied.

This work explores the feasibility of synthesizing active non-platinum group metal oxygen reduction catalysts from naturally abundant peat through a facile one-pot method. The procedure yielded highly porous materials (specific surface area ~1000 m2 g-1) with promising oxygen reduction activity. Onset and half-wave potential values of 0.93 and 0.83 V vs RHE, respectively, were attained in rotating disc electrode experiments for the most active catalyst synthesized using dicyandiamide. Notably, the choice of nitrogen precursor influenced both the porosity and the electrochemical activity. Finally, the best-performing catalyst was analyzed in a rotating ring disc electrode setup, where the results confirmed those obtained in rotating disc electrode measurements.

The oxygen reduction catalyst was synthesized by depositing Pt nanoparticles on carbon black using ethylene glycol as a reducing agent. The synthesized catalyst material contained approximately 60 wt% of Pt, and the average Pt crystallite size was under 3 nm. The catalyst had a micro-mesoporous structure with a specific surface area of 320 m2 g−1. Electrochemical characterization was performed in H2/air fuel cell. The catalyst was deposited on the Nafion membrane or gas diffusion layer using an ultrasonic coating system. The thickness of Teflon gaskets as well as hot pressing conditions were optimized. Lowering catalyst loading on the anode did not show a decrease in electrochemical activity up to 0.05 mg cm−2. However, it was found that the cathode catalyst loading can be reduced only up to 0.60 mg cm−2.

In this study, carbon support material, derived from coffee grounds was used in the preparation of Pt catalysts for polymer electrolyte membrane fuel cell (PEMFC) application. The carbon material was synthesized using ZnCl2 activated pyrolysis method and the Pt nanoparticles were deposited onto carbon support by two methods: using ethylene glycol or hydrogen as a reducing agent. Synthesis of the catalyst materials on coffee ground derived carbon was successful and produced materials with desirable physical and electrochemical properties. Synthesis through the ethylene glycol reduction method, with catalyst material deposited on the gas diffusion layers and additional Nafion layers, produced the most catalytically active material with an electrochemically active surface area value of 63 mPt 2 gPt −1 and catalytic performance of: current density was 0.56 A cm−2 at 700 mV and maximum power density was 0.56 W cm−2. Methods of boosting PEMFC performance through deposition of catalyst material and adding additional Nafion layers were effective and assisted in increasing the overall PEMFC performance.

The self diffusion mechanisms for adsorbed H2 in different porous structures are investigated with in situ quasi elastic neutron scattering method at a temperature range from 50 K to 100 K and at various H2 loadings. The porous structures of the carbon materials have been characterized by sorption analysis with four different gases and the results are correlated with previous in depth analysis with small angle neutron scattering method. Thus, an investigation discussing the effect of pore shape and size on the nature of adsorbed H2 self diffusion is performed. It is shown that H2 adsorbed in nanometer scale pores is self diffusing in two distinguishable timescales. The effect of the pore, pore wall shape and corrugation on the fraction of confined and more mobile H2 is determined and analyzed. The increased corrugation of the pore walls is shown to have a stronger confining effect on the H2 motions. The difference of self diffusional properties of the two H2 components are shown to be smaller when adsorbed in smoother walled pores. This is attributed to the pore wall corrugation effect on the homogeneity of formed adsorbed layers

Electrooxidation of methanol is an essential topic in developing direct methanol fuel cells, and numerous catalyst materials have been studied for this application. 1–3 Among other materials, the platinum-based composite catalysts containing rare earth metal oxides on various support materials have shown promising properties for methanol oxidation and implementation for direct methanol fuel cells.1–3 In this study, platinum-praseodymium oxide nanocatalyst on carbon aerogel support for methanol oxidation was synthesized. The material was electrochemically characterized using rotating disk electrode, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy methods. X-ray diffraction, specific surface area measurements, thermogravimetric analysis, and high-resolution scanning electron microscopy with energy dispersive X-ray analysis were used to determine the physical properties of the material. The catalyst was synthesized by depositing platinum4 on a pyrolyzed organic aerogel doped with Pr(NO3)3 5,6. Synthesized nanocatalyst material contained 21 wt% of Pt and 20 wt% of PrOx. This material has micro-mesoporous structure with surface area of 230 m2 g−1, micropore area of 70 m2 g−1, total pore volume of 0.62 cm3 g−1 and micropore volume of 0.032 cm3 g−1. Pt and PrOx particles were uniformly dispersed on the supporting carbon aerogel-derived material. Electrochemical measurements showed that the studied material has an electrochemically active surface area of 54 mPt 2 gPt −1, which is noticeably higher than that for commercial Pt-Vulcan catalyst (17 mPt 2 gPt −1) and comparable with similar composite catalyst materials containing rare earth metal oxides (from 45 mPt 2 gPt −1 up to 61 mPt 2 gPt −1).3 For methanol electrooxidation the synthesized material showed high current density peaks in both anodic (310 A gPt −1) and cathodic (240 A gPt −1) potential sweeps. These current densities are higher than measured for commercial Pt-Vulcan catalyst (for the peaks in both anodic (178 A gPt −1) and cathodic (167 A gPt −1) potential sweeps). Furthermore, the synthesized material demonstrated the ability of preserving higher catalytic activity (0.33 A gPt −1) than the commercial Pt-Vulcan catalyst (0.07 A gPt −1) after working on a fixed potential of ‒0.2 V vs RHE for an extended period of time (30 min). While these results outstand the catalytic activity of some similar catalyst materials containing praseodymium,1,7,8 higher current densities on both cathodic and anodic potential sweep have been measured with Pt-PrOx catalyst deposited on carbon black Vulcan XC-72R.3 These characteristics show good suitability of the developed nanocatalyst for methanol oxidation in direct methanol fuel cells. This study shows the potential of nanocatalysts containing rare earth metal oxides and catalyst on the carbon aerogel support for methanol electrooxidation. These materials could be further investigated for the electrooxidation for ethanol or other organic fuels. Acknowlegements This work was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), the Estonian Energy Technology Program: SLOKT10209T “Nanomaterials – research and applications (NAMUR)” project 3.2.0304.12-0397and Personal Research Grant PRG676. References Z. Tang and G. Lu, J. Power Sources, 162, 1067–1072 (2006). P. Valk et al., J. Electrochem. Soc., 165, F315–F323 (2018). P. Valk et al., J. Electrochem. Soc., 166, F1062 (2019). C. Galeano et al., J. Am. Chem. Soc., 134, 20457–20465 (2012). K. Kreek, M. Kulp, M. Uibu, A. Mere, and M. Koel, Oil Shale, 31, 185–194 (2014). K. Kreek et al., J. Non-Cryst. Solids, 404, 43–48 (2014). A. O. Neto et al., J. Alloys Compd., 476, 288–291 (2009). L. Chen, J. Hu, and J. S. Foord, Phys. Status Solidi A, 209, 1792–1796 (2012).

The utilisation of fuel cells in everyday life is of critical importance for the introduction of clean energy and departure from carbon-based economy. The oxygen reduction reaction (ORR) rate on the cathode is the key factor for effective polymer electrolyte membrane fuel cells. Therefore, novel cathode catalysts have to be designed to reduce the ORR over voltage. One of the most efficient ways to increase the ORR rate is to use nitrogen doping of carbon materials.1 Such materials are also promising for applications in supercapacitors and other energy storage devices.2 In this work, experimental results based on a nitrogen-doped reduced graphene oxide are presented. The nitrogen-doped reduced graphene oxide has been produced by Sea Further SARL using a biological micro-organisms and non-toxic chemicals.3 The material has been characterised by several physical methods: particle size distribution analysis, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, gas adsorption method, and electrical conductivity measurements. X-ray diffraction data reveal the presence of peaks characteristic to reduced graphene oxide. The specific surface area of the bulk material is around 2.4 m2 g− 1 based on the nitrogen adsorption method. The bulk sample, in powder form, exhibited considerable specific conductance under pressure. Additionally, electrochemical measurements have been conducted in 0.1 M HClO₄ and 0.1 M KOH solutions. The electrochemical stability, capacitive behaviour, and ORR activity of nitrogen-doped reduced graphene oxide have been determined using cyclic voltammetry, rotating disc electrode and electrochemical impedance spectroscopy methods. The material under discussion has a good electrochemical stability within the investigated potential region in both media. The measurement data show that the ORR kinetics in alkaline media is much faster than in acidic media. Surprisingly, this material has a high gravimetric capacitance. Therefore, nitrogen-doped reduced graphene oxide has high potential for energy storage devices and is promising co-catalyst material in fuel cell. Acknowledgements This work was supported by the EU through the European Regional Development Fund under project TK 141 “Advanced materials and high-technology devices for energy recuperation systems” (grant number 2014 2020.4.01.15 0011); and by the Estonian Research Council (grant number PUT PRG 676). References N. Daems, X. Sheng, I.F.J. Vankelecom, and P.P. Pescarmona, J. Mater. Chem. A, 2, 4085 (2014). N.A. Elessawy, J.E. Nady, W. Wazeer, and A.B. Kashyout, Sci. Rep., 9, 1129 (2019). V. Iakimov, International Patent Application No. WO2021/059152, WIPO, April 1st 2021.

Carbons are important in a multitude of applications, and thus, the reversible control of carbon structures is of high interest. Here we report the reversible formation of graphitic structures with three distinct interlayer distances in case of two carbide-derived carbons (CDCs) loaded under hydrogen pressure observed with in situ neutron scattering methods. The formation of these graphitic structures determined with in situ neutron diffraction is brought forth by the confinement of H2 in the porous structure when the temperature, T, is increased from T = 20 K–50 K under H2 loading from 68 mbar to 10 bar. The confinement of the desorbing H2 causes the pressure to increase inside the CDC structure and this increase of pressure is the cause for the reversible formation of graphitic domains. The confinement of H2 at T = 50 K is possible due to the presence of ultramicropores and suitable curved carbon structures. The three distinct formed graphitic domains correspond to a highly pressurized, conventional highly ordered graphitic, and disoriented graphitic domains with possible H2/H intercalation. In situ quasi-elastic neutron scattering and gas adsorption methods are used to determine the H2 transport properties and interactions with the CDCs.

Properties of the adsorbed hydrogen phase have been studied for hydrogen adsorption in three carbide derived carbons: SiC-CDC, steam/CO2 activated SiC-CDC and TiC-CDC. Using the excess hydrogen uptake isotherm at hydrogen pressures above 120 MPa where adsorption has finished, the adsorbate volume has been determined and the adsorbate density has been calculated at ambient temperatures. Absolute adsorption isotherms have been constructed by assuming the adsorbate volume is equivalent to the pore volume and is therefore constant. This study indicates that all three CDCs had the same maximum adsorbate density, with the adsorption proportional to the total pore volume.

The influence of the synthesis conditions on the formation of the porous and the graphitic structure of carbon materials was investigated on Mo2C-derived carbon materials synthesized at different temperatures (Tsyn from 700 to 1000 °C). Contrast matched small-angle neutron scattering method was used to obtain explicit information about the pore and pore wall structure of the carbons. It was found that carbons formed at lower Tsyn exhibit prevalently nano-scale cylindrical geometry and an increase in Tsyn promotes the formation of slit-like structures. Additionally, partial contrast matching was used, which effectively made the pore walls wider, enabled to „hide“ the smaller pores, exposing in greater detail the geometries of larger mesopores. The geometry of larger structures (e.g. pores and pore walls) changes from mixed cylindrical and slit-like to completely slit-like with the increase of Tsyn. The observed change of the geometries, expressed by the increase in the dimensionality parameter, that increases from 1.2 to 1.8, empirically correlates with the decrease in the disorder between graphitic layers. Thus, we conclude that the cylindrical structures are caused by the curvature in graphitic layers formed at lower Tsyn (≤800 °C).

Extensive research is currently being conducted in the field of non-platinum group metal oxygen reduction catalysts for low-temperature fuel cells1,2. Many of the synthesis methods used to produce these novel materials involve grinding the precursors in a planetary ball mill3,4. Consequently, more information is needed to understand how this procedure affects the physical properties of the resulting carbon-based materials. Additionally, it is crucially important to investigate the influence of the physical properties on the electrochemical performance of the electrocatalysts. In this work, several Fe-N/C type electrocatalysts were synthesized from silicon carbide derived carbon via ball milling. A number of parameters, such as grinding mode and ball diameter, were changed in order to study their effect on both the physical and electrochemical properties of the Fe-N/C catalysts. The main characterization methods used in this study were N2-sorption and laser diffraction, which provide insight into the pore and particle size distributions of the materials, respectively. From the rotating disc electrode measurements it is clear that highly active Fe-N/C catalysts can be successfully synthesized using a facile two-step process involving ball milling and pyrolyzing. Changing the ball milling parameters has a considerable effect on both the surface morphology as well as particle size distributions of the studied Fe-N/C catalysts. As a final step, the importance of these changes in the physical properties was studied in a single cell experimental setup. B.-Y. Song, M.-J. Li, Y.-W. Yang, and Y.-L. He, J. Clean. Prod., 249, 119314 (2020) http://www.sciencedirect.com/science/article/pii/S0959652619341848. D. Banham, J.-Y. Choi, T. Kishimoto, and S. Ye, Adv. Mater., 31, 1804846 (2019) https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201804846. S. Ratso et al., ACS Appl. Energy Mater., 2, 7952–7962 (2019) https://doi.org/10.1021/acsaem.9b01430. M. J. Workman et al., J. Power Sources, 348, 30–39 (2017) http://www.sciencedirect.com/science/article/pii/S0378775317302410. Figure 1

Hydrogen adsorption in highly porous carbon with well-defined pores, with three different shapes, and different sizes ranging from sub-to nanometers is investigated. Using a combined approach of volumetric gas adsorption method and in-situ quasi-elastic neutron scattering method the relationship between final macroscopic intake properties, details of the local adsorbent structure and the molecular behaviour of confined hydrogen are established. It is shown that sub-nanometer pores of spherical and cylindrical shape strongly limit the diffusion of H2, and thus, enhance the H2 storage capability of carbons with well-tailored pore structure. In mesoporous carbide-derived carbon, the formation of a hydrogen layer with reduced mobility close to the pore walls is observed. With the increase in the amount of confined hydrogen and the occupation of the centre pore area, the mobility of confined hydrogen increases in a jump–like fashion. Surprisingly, the increase of hydrogen diffusion is also observed at higher hydrogen loadings, indicating that cooperative H2–H2 interactions might play a role.

Different micro–mesoporous carbons derived from d-glucose (GDC), granulated white sugar (WSDC) and highly decomposed Estonian peat (PDC) were synthesized using hydrothermal carbonization and direct activation methods. The resulting carbonaceous materials were activated using chemical (KOH and ZnCl2) and physical (CO2) activation methods. The electrochemical characteristics of the electrical double-layer capacitors (EDLCs) based on 1 M Et3MeNBF4 solution in acetonitrile and EtMeImBF4 were measured using two-electrode cells. The EDLCs assembled had specific capacitances from 20 up to 158 ± 18 F g−1 (in EtMeImBF4) and phase angle values from − 65° to − 88° (at low frequencies). The characteristic time constant values vary more than 10 times. Applying constant power discharge method, very high energy and power densities (34 W h kg−1 at 10 kW kg−1) for activated carbon powders-based EDLCs have been measured. Fitting of impedance data showed that enhanced mesoporosity reduces the adsorption and mass-transfer resistance values.

Carbon supported platinum catalysts for proton exchange membrane fuel cell (PEMFC) applications have been studied intensively in the scientific community.1,2 The catalytic activity of the catalyst depends on the characteristics of the carbon support material3 and on the Pt depositing method4,5. The aim of the study was to investigate the oxygen reduction reaction (ORR) on Pt nanoparticles deposited on peat-derived carbon. The Pt nanoparticles were deposited on the carbon support material by three different methods using NaBH4 (NBH), ethylene glycol (EG) and isopropyl alcohol (IA) as a reducing agent. The studied materials were characterized using N2 sorption, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Structure of the platinum nanocatalyst on carbon support was also studied using scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). For electrochemical characterization, the electrochemically active surface area (ECA) of the materials were measured in a three-electrode system (0,1 M HClO4) and in a completed PEMFC. The ORR kinetics of the materials were studied by the rotating disk electrode (RDE) method as well as in a PEMFC configuration. As a result, it was found that the higher the ECA of the material, the higher the catalytic activity. The catalytic activity of the synthesized materials increases in order: IA < NBH < EG. ECA of the materials increases in the same order. Also, the special surface area of the materials increases in the same order. The catalytic activities of the synthesized materials were compared to a commercial catalyst material, 60% Pt on HSA Ketjenblack. References O. Z. Sharaf and M. F. Orhan, Renew. sust. energ. rev., 32, 810–853 (2014). Y. Wang, K. S. Chen, J. Mishler, S. C. Cho, and X. C. Adroher, Appl. Energ., 88, 981–1007 (2011). S. Sharma and B. G. Pollet, J. Power Sources, 208, 96–119 (2012). S. Sepp et al., Electrochim. Acta, 203, 221–229 (2016). P. Valk et al., J. Electrochem. Soc., 165, F315–F323 (2018). Acknowledgements The author thanks the European Union Regional Development Fund for the financial support of the project TK141 “Innovative materials and high-tech equipment for energy recovery systems” (2014-2020.4.01.15-0011); the Estonian Research Agency project (personal research support group grant project No. PRG676) and the Estonian Energy Technology Program: SLOKT10209T “. Nanomaterials – research and applications (NAMUR)” project 3.2.0304.12-0397. The author also thanks the private limited company AuVe Tech.

A functioning hydrogen economy requires efficient ways of producing and utilizing hydrogen via electrolyzers and fuel cells. The commercialization of these devices is well underway but their considerable capital costs still inhibit faster adoption by society1,2. One pathway towards more inexpensive devices is by tackling their respective bottlenecks, the oxygen evolution and reduction reactions, which currently require catalyst materials comprised of scarce precious metals. Intensive research is being conducted to introduce and develop suitable replacements for these catalysts. In this field, non-platinum group metal (NPGM) type catalysts have gained significant attention2,3. We present several NPGM-type oxygen electrocatalysts synthesized by modifying peat-derived carbon with nitrogen and different combinations of transition metals (Fe, Co, Ni). The obtained catalysts were characterized with various methods to elucidate their structure-reactivity relations. Namely, SEM-EDS was used to confirm that the modification of peat-derived carbon was successful. Additionally, the various metal alloy species found in the catalysts were identified via X-ray diffraction analysis. The excellent bifunctional electrocatalytic activity of the peat-based materials towards oxygen evolution and reduction was confirmed with rotating disc electrode measurements conducted in a 0.1 M KOH solution. Correlations between the physical and electrochemical properties of the catalysts were established and analyzed. Acknowledgments This work was supported by the EU through the European Regional Development Fund under projects TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), NAMUR “Nanomaterials - research and applications” (3.2.0304.12-0397), PRG676 “Development of express analysis methods for micro-mesoporous materials for Estonian peat derived carbon supercapacitors” (01.01.2020–31.12.2024) and PUT1581 (1.01.2017–31.12.2020). References E4tech, 2021, The Fuel Cell Industry Review 2020. C. Lei, S. Lyu, J. Si, B. Yang, Z. Li, L. Lei, Z. Wen, G. Wu, Y. Hou, ChemCatChem 2019, 11, 5855. L. Osmieri, J. Park, D. Cullen, P. Zelenay, D. Myers, K. Neyerlin, Curr Opin Electrochem 2021, 25, 100627. Figure 1

Herein we demonstrate how peat, abundant and cheap biomass, can be successfully used as a precursor to synthesize peat derived hard carbons PDCs , applicable as electrode materials for sodium ion batteries SIB . The PDCs were obtained by pre pyrolysing peat at 300 800 C, removing impurities with base acid solution treatment and thereafter post pyrolysing the materials at temperatures T from 1000 to 1500 C. By modification of pre and post pyrolysis temperatures we obtained hard carbons with low surface areas, optimal carbonization degree and high electrochemical Na storage capacity in SIB halfcells. The best results were obtained when pre pyrolysing peat at 450 C, washing out the impurities with KOH and HCl solutions and then post pyrolysing the obtained carbon rich material at 1400 C. All hard carbons were electrochemically characterized in half cells vs. Na Na and capacities as high as 350 mA h g 1 at 1.5 V and 250 mA h g 1 in the plateau region E lt; 0.2 V were achieved at charging current density of 25 mA g 1 with an initial coulombic efficiency of 80

Hard carbons have emerged as one of the most promising candidates for high capacity anode materials in sodium-ion batteries (SIB). It has been demonstrated that the degree of graphitization, disorder, and porosity of obtained hard carbons have an enormous effect on capacity.1 Various biomass precursors (banana peels, peanut shells, leaves, etc.) have been used for obtaining hard carbons, which have shown promising results as SIB anodes.2–4 In this study, peat was used as the precursor for obtaining peat-derived hard carbon anode materials (PDCs). Peat has a distinctive advantage as a precursor for its ease of collection. It can be excavated in millions of tons, as opposed to collecting shells or peels of different fruit. Hard carbons were synthesized using three steps – pre-pyrolysis at 300-800 oC, base-acid treatment, and post pyrolysis at 1000-1500 oC (Fig. 1). Each step was deemed necessary to improve the capacity of obtained hard carbon material (Fig. 1a). The materials were labeled as follows: PDC – pre-pyrolysis temperature – post-pyrolysis temperature A (A appended if KOH-HCl treatment was used).5 The structure of hard carbon materials was investigated with XRD, SEM-EDX, TEM, Raman spectroscopy, and laser powder diffraction methods. The specific surface area was examined by gas sorption analysis (with N2 and Ar). XRF was used to determine the elemental composition of hard carbon materials before and after the KOH-HCl treatment. TGA was performed to evaluate the burn-off of peat’s organic content during pre-pyrolysis. Cycling performance of hard carbon electrodes was investigated using the galvanostatic charge-discharge method at current densities ranging from 25 to 2000 mA g-1 and cyclic voltammetry at a potential sweep rate of 0.1 mV s-1. NaClO4 in EC:DEC (1:1) and NaPF6 EC:PC (1:1) were used as electrolytes to compare two rather common electrolytes and their effect on capacity (Fig. 1b). The highest capacities were achieved for PDC-450-1400 A. The constant current measurements show very high capacities of 350 mAh g -1 with a plateau region (E < 0.2 V vs. Na/Na+) of 250 mAh g-1 at the current density of 25 mA g -1. At the current density of 50 mA g-1, a capacity of 328 mAh g-1 with a plateau region of 243 mAh g -1 was achieved. Long-term stability of PDC-450-1400 A was also demonstrated, after 130 charge-discharge cycles at the current density of 25 mA g-1, the capacity stabilized at 280 mAh g-1 with the initial capacity of 320 mAh g-1. Overall, the highest capacities were achieved with materials that had the lowest impurity contents and specific optimal physical properties – low surface areas of around 6 m2 g-1, broad 002 reflexes in XRD diffractograms, interlayer spacing of about 3.9 Å and optimal I D/I G values of approximately 1.50. These characteristics might indicate the existence of local graphitic domains and therefore explain the high capacities.5 Acknowledgments This work was supported by ‘Strengthening of sectoral R&D’ project LLTOM17351, by EU through the European Regional Development Fund project 2014-2020.3.01.15-0011 and Personal Research under Grant PRG676. References I. El Moctar et al., Functional Materials Letters, 11, 1830003 (2018). E. M. Lotfabad et al., ACS Nano, 8, 7115–7129 (2014). J. Ding et al., Energy Environ. Sci., 8, 941–955 (2015). H. Li et al., ACS Appl. Mater. Interfaces, 8, 2204–2210 (2016). A. Adamson et al., RSC Adv., 10, 20145–20154 (2020). Figure 1