H2O2 is a valuable, environmentally friendly oxidizing agent with a wide range of uses from the provision of clean water to the synthesis of valuable chemicals. The on-site electrolytic production of H2O2 would bring the chemical to applications beyond its present reach. The successful commercialization of electrochemical H2O2 production requires cathode catalysts with high activity, selectivity, and stability. In this Perspective, we highlight our current understanding of the factors that control the cathode performance. We review the influence of catalyst material, electrolyte, and the structure of the interface at the mesoscopic scale. We provide original theoretical data on the role of the geometry of the active site and its influence on activity and selectivity. We have also conducted a series of original experiments on (i) the effect of pH on H2O2 production on glassy carbon, pure metals, and metal–mercury alloys, and (ii) the influence of cell geometry and mass transport in liquid half-cells in com...

/pdf/toward-the-decentralized-electrochemical-production-of-h2o2-1ad226masv.pdf

Toward the Decentralized Electrochemical Production of H2O2: A Focus on the Catalysis

H2O2 production by electroreduction of O2 is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost-effective electrocatalysts for H2O2 synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H2O2 from O2 reduction. It exhibited high activity for O2 reduction and good H2O2 selectivity (95.0–70.2 %, most of them >90.0 % at pH 1–4 and >80.0 % at pH 7). High-yield H2O2 generation has been achieved on HPC with H2O2 concentrations of 222.6–62.0 mmol L−1 (2.5 h) and corresponding H2O2 production rates of 395.7–110.2 mmol h−1 g−1 at pH 1–7 and −0.5 V. Moreover, HPC was energy-efficient for H2O2 production with current efficiency of 81.8–70.8 %. The exceptional performance of HPC for electrosynthesis of H2O2 could be attributed to its high content of sp3-C and defects, large surface area and fast mass transfer.

High‐Yield Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction by Hierarchically Porous Carbon

Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M-N-C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic activity of M-N-C materials toward four-electron oxygen reduction reaction (ORR) to H2O is a mainstream line of research for replacing platinum-group-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H2O2, a future green "dream" process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H2O2 production over a series of M-N-C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M-Nx sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M-N-C catalysts on the electrocatalytic activity/selectivity for ORR (H2O2 and H2O products) and H2O2 reduction reaction (H2O2RR). Co-N-C catalyst was uncovered with outstanding H2O2 productivity considering its high ORR activity, highest H2O2 selectivity, and lowest H2O2RR activity. The activity-selectivity trend over M-N-C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four- and two-electron ORR. The predicted binding energy of HO* intermediate over Co-N-C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H2O2 productivity over Co-N-C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide gcatalyst-1 h-1 at a current density of 50 mA cm-2.

Activity–Selectivity Trends in the Electrochemical Production of Hydrogen Peroxide over Single-Site Metal–Nitrogen–Carbon Catalysts

Electrochemical hydrogen peroxide (H2O2) production by two-electron oxygen reduction is a promising alternative process to the established industrial anthraquinone process. Current challenges relate to finding cost-effective electrocatalysts with high electrocatalytic activity, stability, and product selectivity. Here, we explore the electrocatalytic activity and selectivity toward H2O2 production of a number of distinct nitrogen-doped mesoporous carbon catalysts and report a previously unachieved H2O2 selectivity of ∼95–98% in acidic solution. To explain our observations, we correlate their structural, compositional, and other physicochemical properties with their electrocatalytic performance and uncover a close correlation between the H2O2 product yield and the surface area and interfacial zeta potential. Nitrogen doping was found to sharply boost H2O2 activity and selectivity. Chronoamperometric H2O2 electrolysis confirms the exceptionally high H2O2 production rate and large H2O2 faradaic selectivity f...

Efficient Electrochemical Hydrogen Peroxide Production from Molecular Oxygen on Nitrogen-Doped Mesoporous Carbon Catalysts

Electrocatalytic reduction is a promising approach to remediate nitrate (NO3–), one of the world’s most widespread water pollutants. In the present work, we elucidate activity and selectivity trend...

Activity and Selectivity Trends in ElectrocatalyticNitrate Reduction on Transition Metals

Preparation and electrochemical studies of metal–carbon composite catalysts for small-scale electrosynthesis of H2O2

PtxIr100–x thin films (8 nm thick) were deposited on MgO(100) substrates by pulsed laser deposition at 600 °C. As shown by X-ray diffraction and X-ray photoelectron spectroscopy analyses, the formation of fcc bulk and surface PtIr solid solution was observed over the whole compositional range despite the large miscibility gap exhibited by these elements below ca. 1000 °C. Moreover, pole figures indicate that all films exhibit a Pt(001)[010]//[010](001)MgO cube-on-cube epitaxial relationship, which is consistent with AFM images. Cyclic voltammetry measurements performed in alkaline solutions confirmed both the presence of Ir atoms at the surface and the (100) surface orientation of all PtxIr100–x surfaces. The highest electrocatalytic activity for the electrooxidation of NH3 was observed for the Pt74Ir26(100) surface with a current density of ca. 1.0 mA cm–2 at 0.71 V vs RHE, which is 25% higher than that on Pt(100). The reasons underlying this behavior are discussed.

Tuning Pt–Ir Interactions for NH3 Electrocatalysis

We study the adsorption of borohydride on Au and Au-based alloys (Au3M with M = Cr, Mn, Fe, Co, and Ni) using first-principles calculations based on spin-polarized density functional theory. Favorable molecular adsorption and greater adsorption stability compared to pure Au are achieved on Au3M alloys. For these alloys, there is an emergence of unoccupied states in the surface d band around the Fermi level with respect to the fully occupied d band of pure Au. Thus, the derived antibonding state of the sp–d interaction is upshifted and becomes unoccupied compared to pure Au. The B–H bond elongation of the adsorbed borohydride on these alloy surfaces points to the role of surface-parallel (dxy and dx2−y2 states) components of the d-band of the alloying metal M, most pronouncedly in the cases of M = Co or Ni. On the alloy surfaces, B binds directly with the alloying metal, unlike in the case of pure Au where the surface bonding is through the H atoms. These results pose relevant insights into the design of Au-based anode catalysts for the direct borohydride fuel cell.

Structure and stability of borohydride on Au(111) and Au3M(111) (M = Cr, Mn, Fe, Co, Ni) surfaces

Novel organic redox catalyst for the electroreduction of oxygen to hydrogen peroxide

Bimetallic alloys of Pt and Rh or Ir were prepared with pulsed laser deposition (PLD) on a well-ordered MgO(100) substrate, leading to epitaxial growth along the [001] plane, as confirmed by surface analysis techniques. The out-of-equilibrium conditions of PLD allowed the exploration of a range of compositions for which phase separation would instead be expected. The electrochemistry of a series of PtRh and PtIr (100) alloys was investigated in 0.5 M H 2 SO 4 , showing a surprisingly intense electrocatalytic activity towards the reduction of nitrate for a Pt content of 21–42%. These alloys feature a lower reaction overpotential with respect to Rh and Ir while outperforming the pure metals in terms of reduction current. A detailed analysis of the voltammetric features with respect to alloy composition highlighted a correlation between hydrogen desorption and nitrate reduction activity. In addition, an optimal potential range for nitrate reduction, common to PtRh and PtIr alloys, was observed, corresponding to the potential window in which nitrate adsorption coincides with fast reduction of the key reaction intermediate NO ads .

Andrew Wang

Papers

Preparation and electrochemical studies of metal–carbon composite catalysts for small-scale electrosynthesis of H2O2

Tuning Pt–Ir Interactions for NH3 Electrocatalysis

Structure and stability of borohydride on Au(111) and Au3M(111) (M = Cr, Mn, Fe, Co, Ni) surfaces

Novel organic redox catalyst for the electroreduction of oxygen to hydrogen peroxide

Enhanced electrocatalytic nitrate reduction by preferentially-oriented (100) PtRh and PtIr alloys: the hidden treasures of the ‘miscibility gap’