Playing with Fire: Commercialization of a Metal-Supported SOFC Product for Use in Charcoal Cookstoves
Authors: Tucker Michael C , Jacobson Craig P , Carreon Bernard , Charyasatit Jeffrey , Langston Kenny , Taylor Cindy , Manjarrez Jose , Burton Nicholas , LaBarbera Mark 
Published: February 2020

Metal-Supported Solid Oxide Fuel Cells (mSOFC) developed at Lawrence Berkeley National Laboratory (LBNL) and elsewhere exhibit extreme thermal shock tolerance, are mechanically rugged, and withstand deep redox cycling.[1] The cell structure is shown in Figure 1. Point Source Power (PSP) was spun out of LBNL to commercialize portable power consumer products that utilize these advantages of mSOFC technology. PSP’s primary product was the VOTO (Figure 2), designed to operate in charcoal-burning cookstoves prevalent throughout the developing world. The VOTO is fueled by biomass, and heated to 650-850°C operation temperature during cooking, producing a few Watts of electricity. The electricity is stored for later use in a handle with on-board NiMH batteries, a LED lamp, and mobile phone charging port. Technical challenges addressed at PSP include: thermochemistry in the anode chamber, identification of electrochemically-active species, mineral content of wood chars, catalyst selection, and thermal activation of the desired reactions. These have been presented previously.[2] The present paper will discuss various aspects of the complex and challenging development and commercialization of the VOTO product.

Kenya has high mobile phone ownership, relatively low electrification rate, prevalent use of solid cooking fuel, widespread deployment of the Jiko-style charcoal stove (Fig 2), and relatively advanced industrial capabilities relative to its sub-Saharan neighbors. Kenya was therefore a promising choice of first target market. The California-based development team conducted iterative product-generation improvements informed by frequent interaction with end-users, a production team, and sales and distribution networks in Kenya. Early in the development cycle it was discovered that Kenyan charcoal cooking practices result in significantly lower mSOFC operating temperature than the standard protocol adopted at PSP. This resulted in significant design and form-factor changes to the mSOFC stack to increase cell temperature, and required development of catalysts to promote conversion of charcoal to electrochemically-active gaseous fuels at low temperature. It was also found that significant regional differences in charcoal quality exist. This contributed to the decision to provide compacted tablet-cards of high-quality charcoal as part of the product kit, rather than the lower-cost option of encouraging end-users to prepare their own mSOFC fuel from locally-available cooking charcoal. The possibility of mSOFC stack assembly in Kenya also contributed to the flat-pack cell housing design, in which the stack components can be fabricated from sheet metal, shipped flat, and then folded with common hand tools to achieve the final configuration.

Using charcoal as the electrochemically-active fuel and as the cooking fuel (providing heat to the mSOFC stack) is challenging. Several rapid degradation mechanisms are associated with mineral (ash) components in the biomass charcoal. In oxidizing atmosphere, potassium in charcoal reacts with chromium in the stainless steel stack components, creating a volatile compound that is reduced in the cathode, depositing chromium and contaminating the cathode catalyst. Chlorine from the charcoal rapidly corrodes stainless steel in the stack components and mSOFC. Various design improvements were implemented to mitigate these failure mechanisms, including protection of the cathode by a sacrificial shield, and oversizing the charcoal fuel tablets to ensure reducing conditions throughout operation to avoid corrosive ash formation. Even so, mSOFC lifetime under daily use was limited to 2-3 months. This required a product design and business model pivot towards a razor-blade model, with a durable handle containing NiMH batteries and electronic components, and a consumable fuel cell stack.

A detailed cost model for production of the mSOFC stack, durable electronics handle, and charcoal fuel tablets was developed. This model was used to determine impact of labor rates and production volume on cost. This provided guidance in planning for initial production facilities locations, as well as market size required to achieve the desired price target.

Finally, the response to the VOTO from the end-user market and investment community will be summarized.

[1] Progress in Metal-Supported SOFCs: A Review, M.C. Tucker, Journal of Power Sources, 195, 4570-4582 (2010)

[2] Operation of Metal-Supported SOFCs with Charcoal Fuel, M.C. Tucker, M. LaBarbera, C. Taylor, C.P. Jacobson, ECS Transactions, 57, 2929-2937 (2013)

Figure 1