12 Search Results

Low-temperature heat (T<130°C) can be utilized by thermally regenerative batteries (TRBs) for power production, allowing the thermal energy to be converted to storable chemical potential energy. However, TRBs suffer from high ohmic losses and ammonia crossover, which has slowed their development. In this study, we examined how the use of six different membranes influenced TRB performance, determined the most influential membrane parameters, and identified promising membrane candidates that cost-effectively increase TRB performance. Of the six membranes examined, an inexpensive, hydrocarbon CEM (Selemion CMVN) had low ammonia crossover without compromising resistance, resulting in good performance across all metrics studied. A thinmore » anion exchange membrane (Sustainion, 50 microns) showed a high peak power density of 82 mW cm^–2 due to low resistance, but the average power density and energy density were low due to high ammonia flux. Full discharge curves using Selemion CMVN provided an average power density of 26 ± 7 mW cm^–2 with an energy density of 2.9 Wh L^–1, which were large improvements on previous TRBs. A techno-economic analysis showed that Selemion CMVN had the lowest levelized cost of storage ($410 per MWh) at an applied current density of 50 mA cm^–2.« less

Thermally regenerative ammonia batteries (TRABs) can provide energy storage and produce electrical power from low-grade waste heat instead of electricity. The use of all-aqueous copper-based electrolytes has recently produced higher power densities than those achieved using previous TRAB approaches based on reversible metal deposition and dissolution processes, but further gains are possible in power and energy density. We investigated the limitations of power and energy density and how they are impacted by the electrolyte composition and discharge currents. By increasing the ammonia concentration from 1 to 5 M, the power density of the battery increased from 11.2 to 28.5 mWmore » cm^–2, but the energy density decreased from 0.56 to 0.31 Wh L^–1. Increasing discharge current densities from 4 to 12.5 mA cm^–2 increased the average power density during discharge from 2.4 to 5.9 mW cm^–2 without appreciable losses in energy density. Increasing the copper concentration from 0.1 to 0.5 M increased both energy density to 2.15 Wh L^–1 and energy efficiency to 2.2% but did not substantially impact the power density. Furthermore, these results represent the highest performance metrics achieved for a low-grade waste heat to electricity system.« less

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Hydrogen production using two-chamber microbial electrolysis cells (MECs) is usually adversely impacted by a rapid rise in catholyte pH because of proton consumption for the hydrogen evolution reaction. While using a bipolar membrane (BPM) will maintain a more constant electrolyte pH, the large voltage loss across this membrane reduces performance. To overcome these limitations, we used an acidic catholyte to compensate for the potential loss incurred by using a BPM. A hydrogen production rate of 1.2 ± 0.7 L-H₂/L/d (j_max = 10 ± 0.4 A/m²) was obtained using a Pt cathode and BPM with a pH difference (ΔpH = 6.1)more » between the two chambers. This production rate was 2.8 times greater than that of a conventional MEC with an anion exchange membrane (AEM, 0.43 ± 0.1 L-H₂/L/d, j_max = 6.5 ± 0.3 A/m²). The catholyte pH gradually increased to 11 ± 0.3 over 9 days using the BPM and Pt/C, which decreased current production (j_max = 2.5 ± 0.3 A/m²). However, this performance was much better than that obtained using an AEM as the catholyte pH increased to 10 ± 0.4 after just one day. The use of an activated carbon cathode with the BPM enabled stable performance over a longer period of 12 days, although it reduced the hydrogen production rate (0.45 ± 0.1 L-H₂/L/d).« less

Transition metal phosphide catalysts such as nickel phosphide (Ni₂P) have demonstrated excellent activities for the hydrogen evolution reaction, but they have primarily been studied in strongly acidic or alkaline electrolytes. In microbial electrolysis cells (MECs), yet, the electrolyte is usually a neutral pH to support the bacteria. Carbon-supported phase-pure Ni₂P nanoparticle catalysts (Ni₂P/C) were synthesized using solution-phase methods and their performance was compared to Pt/C and Ni/C catalysts in MECs. The Ni₂P/C produced a similar quantity of hydrogen over a 24 h cycle (0.29 ± 0.04 L-H₂/L-reactor) as that obtained using Pt/C (0.32 ± 0.03 L-H₂/L) or Ni/C (0.29 ±more » 0.02 L-H2/L). The mass normalized current density of the Ni₂P/C was 14 times higher than that of the Ni/C, and the Ni₂P/C exhibited stable performance over 11 days. Ni₂P/C may therefore be a useful alternative to Pt/C or other Ni-based catalysts in MECs due to its chemical stability over time.« less