Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss

Abstract

Conventional production of hydrogen requires large industrial plants to minimise energy losses and capital costs associated with steam reforming, water-gas shift, product separation, and compression. Here we present a protonic membrane reformer (PMR) which produces high purity hydrogen from steam methane reforming in a single-stage process with near-zero energy loss. We use a BaZrO 3 -based proton-conducting electrolyte deposited as a dense film on a porous Ni composite electrode with dual function as a reforming catalyst. At 800 °C, we achieve full methane conversion by removing 99 % of the formed hydrogen, which is simultaneously compressed electrochemically up to 50 bar. A thermally-balanced operation regime is achieved by coupling several thermo-chemical processes. Modelling of a small scale (10 kg H 2 day -1 ) hydrogen plant reveals an overall energy efficiency of >87 %. The results suggest that future declining electricity prices can make PMRs a competitive alternative for industrial-scale hydrogen plants integrating CO 2 capture.Membranes that simultaneously enable chemical reaction and product separation hold promise for process intensification 1-3 . Currently, the most energy efficient production pathway for hydrogen from methane combines steam reforming (CH 4 + H 2 O = 3H 2 + CO, ΔH 1073K = 226 kJ mol -1 ) and water-gas shift (CO + H 2 O = H 2 + CO 2 , ΔH 1073K = -34 kJ mol -1 ) in a multistep process 4 , where heat management is crucial. The produced hydrogen is conventionally separated downstream using e.g. pressure swing absorption (PSA) 5 . Alternatively, hydrogen separation can be included in the steam reforming process using hydrogen selective membranes 6,7 with the benefit of simultaneously separating hydrogen while shifting the thermodynamic equilibrium resulting in process intensification. Most practiced membranes are metallic, predominantly based on Pd or Pd-Ag alloys 8 . The separation is driven by the hydrogen partial pressure difference across the membrane, from which it follows that the pressure of the produced hydrogen is low, and further

Detrimental Effect of Sintering Additives on Conducting Ceramics: Yttrium‐Doped Barium Zirconate

“…Not only fuel cells, but other electrochemical devices,i ncluding electrolyzers, [53,54] hydrogen separation [55,56] and methane reforming materials, [57,58] have been fabricated by such a method.H owever,a sc larified in our preliminary experiment (Figure 1), regardless of whether sintering additives were added on purpose or not, NiO in the anode diffused into the electrolyte layer and played the role of the sintering additive. Not only fuel cells, but other electrochemical devices,i ncluding electrolyzers, [53,54] hydrogen separation [55,56] and methane reforming materials, [57,58] have been fabricated by such a method.H owever,a sc larified in our preliminary experiment (Figure 1), regardless of whether sintering additives were added on purpose or not, NiO in the anode diffused into the electrolyte layer and played the role of the sintering additive.…”

“…Currently,t he mostc ommons tructure for BZY20 electrolytebased cells is an anode-supported one, which is composed of at hick anode layer and at hin electrolyte layer,c oupled with a co-sintering process and an optionals intering additive, which allowst he implementation of electrolyte layers thinned to tens of micrometers with minimized loss of ohmic resistance. Not only fuel cells, but other electrochemical devices,i ncluding electrolyzers, [53,54] hydrogen separation [55,56] and methane reforming materials, [57,58] have been fabricated by such a method.H owever,a sc larified in our preliminary experiment (Figure 1), regardless of whether sintering additives were added on purpose or not, NiO in the anode diffused into the electrolyte layer and played the role of the sintering additive. Al iterature review revealed that the co-sintered cells have a conductivity of approximately 0.001-0.003Scm À1 (Table1), in accordance with the resultsi nt his work;t hat is, the BZY20 sample dopedw ith 1o r2wt %N iO had ac onductivity (mainly proton conduction) lower than 0.004 Scm À1 in wet hydrogen (Figure 9).…”

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

“…This is useful to model the thermal expansion of certain electrode materials, requiring high ionic and electronic conductivity. For instance, for mixed protonic-electronic conduction, a cermet consisting of Ni and BaCe 0.9−x Zr x Y 0.1 O 3−δ -providing electronic and protonic conductivity, respectively-can typically be used in a proton ceramic electrochemical cell [7,8,10]. These models can also be applied to polycrystalline single-phase materials composed of anisotropic grains with random crystal orientations and thermal expansion coefficients.…”

Gas Humidification Impact on the Properties and Performance of Perovskite‐Type Functional Materials in Proton‐Conducting Solid Oxide Cells

“…If electronic transport is comparable with (or higher than) the ionic one, electrode‐free membranes for hydrogen‐separation reactors and electrode materials for electrode‐based SOCs can be purposefully designed . Unconventional proton transport for oxide materials allows the unique processes to be also carried out, for example, a precise H/D/T‐isotope analysis, conversion of harmful (NO x ) or widely available compounds (CO 2 ) to harmless and valuable products (N 2 , CO), conversion of saturated hydrocarbon (CH 4 , C 2 H 6 ) to unsaturated or aromatic compounds (C 2 H 4 , C 6 H 6 ), hydrogen compression, etc …”